System Requirements Document for venus-start

1. Introduction

venus-start is a simple, single-page calculator design for people who need fast, legible everyday arithmetic without distraction. The product is a self-contained calculator instrument: users enter numbers and operators, view the active expression and result, correct or clear the current calculation, and continue working on the same page.

The current product scope is intentionally narrow. venus-start is one public calculator page and no additional pages, modules, user accounts, history, saved calculations, or adjacent productivity features are included.

2. System Overview

venus-start delivers a custom, anonymous calculator interface as a single-page web experience. The Calculator User operates the calculator directly through a structured numeric and operator keypad. The page displays the current expression and an evaluated result in a highly legible instrument-style display.

Current accepted behavior includes:

• Entering numeric values.
• Selecting arithmetic operators.
• Evaluating a calculation.
• Reading the current expression and result.
• Clearing or correcting the current calculation.
• Recovering from an invalid calculation state without leaving the page.

The calculator is the entire current product. There is exactly one custom application page: Calculator.

2a. Product Interpretation and Delivery Boundary

The Calculator is a publicly accessible, anonymous entry surface. No sign-in, registration, account continuity, role-based permissions, external provider surface, or external destination is required.

The Calculator page owns the complete current interaction lifecycle:

• Number and operator entry.
• Current-expression display.
• Result display.
• Calculation evaluation.
• Clear and correction actions.
• Invalid-input feedback and recovery.

The product must remain a simple single-page design. Navigation to additional product pages, saved history, memory-management workflows, financial advice, unit conversion, scientific operations, account management, sharing, and other calculator variants are outside the current delivery boundary.

2b. Page Content and Component Coverage

Calculator

• Access and page purpose

  • Public anonymous page with no account or identity requirement.
  • The sole product destination and the complete calculator workspace.
  • Supports everyday arithmetic in one uninterrupted interaction context.

• Instrument frame and metadata

  • Rectangular calculator chassis with a narrow vertical metadata rail on desktop.
  • Metadata rail includes VENUS—START, CALCULATOR 01, and READY.
  • On mobile, metadata collapses into a single top rule while retaining the calculator’s instrument identity.
  • A bottom calibration strip presents local time, memory state, and a small dot-grid indicator as non-navigational instrument metadata.
  • The memory-state indicator is presentational status only; it does not introduce memory storage or memory operations.

• Calculation display

  • Wide cream display band positioned above the keypad.
  • Small expression line shows the entered number-and-operator sequence.
  • Large right-aligned result display shows the current entered value or evaluated result.
  • An amber status square indicates calculator readiness or an error state.
  • Display values use tabular figures for stable numeric alignment.

• Keypad

  • One ruled, four-column keypad panel.
  • Numeric keys enable number entry.
  • Operator keys enable arithmetic operation selection.
  • Operator controls include visible secondary labels: ADD, SUB, MULT, and DIV.
  • A distinct orange equals key initiates evaluation.
  • Utility controls support clearing or correcting the current calculation.
  • Key labels and spacing must make each control’s arithmetic purpose unambiguous.

• Calculation interaction states

  • Ready: Calculator is available for the user to begin entering a calculation.
  • Entry: The current number and expression update as the user enters values and operators.
  • Evaluated: The display shows the calculation result and retains the result for continued calculation or clearing.
  • Error: The display identifies an invalid calculation state, such as division by zero, without producing a misleading result.
  • Recovered: Clear or correction returns the calculator to a usable ready or entry state.

• Feedback and recovery

  • Pressed keys visibly darken and depress to confirm input.
  • Result changes use a brief digit wipe to provide legible confirmation.
  • If an expression cannot be evaluated, the page displays an error state and keeps clear/correction controls available.
  • The user can clear the active calculation or correct the current entry and continue on the same page.

3. Functional Requirements

FR-01 — Use the Single-Page Calculator

As a Calculator User, I should be able to open and use the Calculator on one public page so that I can perform arithmetic without navigating elsewhere.

• Provenance: explicit
• Access state: Anonymous public access; no account or sign-in is required.
• Trigger/input: The user opens venus-start.
• Behavior: The system presents the Calculator as the sole application page and primary interaction surface.
• Observable result: The user can see the calculator display, keypad, utility controls, and instrument metadata.
• Failure/recovery: If an interactive control is temporarily unavailable during initialization, the page must preserve the calculator frame and restore usable controls when initialization completes.
• Continuation: The user enters a calculation using the keypad.
• Acceptance criteria:
  • The delivered product contains exactly one page named Calculator.
  • The Calculator is the public entry surface.
  • No additional page, module, or navigational destination is included.
  • The design remains simple and focused on calculator use.

FR-02 — Enter Numbers and Operators

As a Calculator User, I should be able to enter numbers and arithmetic operators so that I can form a calculation.

• Provenance: required_inference
• Rationale: Number and operator entry is indispensable to a usable calculator and is established by the accepted Calculator page contract.
• Access state: Anonymous public access.
• Trigger/input: The user selects numeric keys and operator keys.
• Behavior: The system appends or updates the active calculation expression using the user’s selections.
• Observable result: The expression line and result display visibly reflect the active entry state.
• Failure/recovery: If a key input would create an unsupported or incomplete expression state, the calculator must not present it as a valid result. The user can correct the entry or clear the calculation.
• Continuation: The user may enter additional values and operators, evaluate the expression, or correct/clear the active calculation.
• Acceptance criteria:
  • Numeric keys provide number entry.
  • Operator keys provide arithmetic operation selection.
  • Operator controls visibly distinguish addition, subtraction, multiplication, and division.
  • The current expression is visible above the primary result display.
  • Input remains within the Calculator page.

FR-03 — Evaluate a Calculation

As a Calculator User, I should be able to evaluate my entered arithmetic expression so that I can obtain a result.

• Provenance: required_inference
• Rationale: Evaluation and result display are indispensable to fulfilling the accepted calculator purpose and are established by the Calculator page contract.
• Access state: Anonymous public access.
• Trigger/input: The user selects the equals control after entering an evaluable arithmetic expression.
• Behavior: The system evaluates the active expression using the selected arithmetic operations.
• Observable result: The large display updates to show the calculated result, while the expression remains visible as calculation context.
• Failure/recovery: If the expression is invalid or cannot be evaluated, including division by zero, the system must show an error state instead of a misleading result. The user can correct or clear the active calculation.
• Continuation: After a successful result, the user may continue calculating from the visible result, begin a new expression, or clear the calculation.
• Acceptance criteria:
  • A dedicated equals control evaluates a valid entered expression.
  • The result is visible in the primary result display.
  • Division by zero produces an explicit error state rather than a numeric result.
  • Evaluation does not require navigation, sign-in, or an external service.

FR-04 — Clear or Correct the Current Calculation

As a Calculator User, I should be able to clear or correct the current calculation so that I can recover from an unwanted entry or start again.

• Provenance: required_inference
• Rationale: Clearing and correction are required by the accepted Calculator page contract and are necessary recovery mechanics for a usable calculator.
• Access state: Anonymous public access.
• Trigger/input: The user selects a clear or correction utility control.
• Behavior: The system removes the active calculation or corrects the current entry according to the selected utility action.
• Observable result: The expression and display update to the corrected state or return to the ready state.
• Failure/recovery: Utility controls remain available during invalid-expression and calculation-error states so the user can recover without reloading or leaving the page.
• Continuation: The user can enter a new calculation or continue the corrected calculation.
• Acceptance criteria:
  • The Calculator provides an explicit means to clear the current calculation.
  • The Calculator provides an explicit means to correct the current entry.
  • Clearing returns the calculator to a ready state.
  • Correction and clearing are usable after an evaluation error.

FR-05 — Receive Clear Input and Result Feedback

As a Calculator User, I should receive immediate, legible feedback for keypad input and display changes so that I can use the calculator confidently.

• Provenance: explicit for design direction; required_inference for interaction feedback as a usable calculator mechanic.
• Access state: Anonymous public access.
• Trigger/input: The user presses a keypad control or completes a calculation.
• Behavior: The pressed key darkens instantly, depresses by 2px, and returns in 120ms. Display changes use a brief 80ms digit wipe from bottom to top.
• Observable result: The user can associate each action with an immediate visual response and an updated display state.
• Failure/recovery: If motion is reduced or unavailable, the system must preserve static pressed-state contrast and an immediate readable display update.
• Continuation: The user continues entering, evaluating, correcting, or clearing the calculation.
• Acceptance criteria:
  • Keypress feedback is mechanical and restrained.
  • No bouncing, elastic motion, floating motion, particle effects, gradients, or ambient animation is used.
  • Display updates remain readable whether motion is enabled or reduced.

4. User Personas

Calculator User

• Product context: A person opening venus-start to complete a straightforward arithmetic calculation using a focused, single-page tool.
• Primary goal: Obtain a correct result quickly and read it at a glance.
• Distinct accepted responsibilities:
  • Enter numbers.
  • Choose arithmetic operators.
  • Evaluate the active expression.
  • Read the current expression and result.
  • Clear or correct an unwanted or invalid entry.
• Relevant inputs and decisions: The user decides which numeric values and arithmetic operations to enter, when to evaluate, and whether to continue, correct, or clear the active calculation.
• Interaction with other accepted participants: None. The calculator interaction has no additional active human participant.
• Observable success: A correct, legible result appears on the Calculator page, or an invalid expression is clearly identified and can be corrected or cleared without leaving the page.
• Role provenance: required_inference. This is the sole active human role supported by the accepted single-page calculator scope.

5. Core User Flows

Flow 1 — Perform an Arithmetic Calculation

1. The Calculator User opens the public Calculator page.
2. The Calculator page presents the ready display, keypad, expression line, and result display.
3. The Calculator User selects numeric keys to enter the first value.
4. The Calculator updates the visible expression and display to reflect the entered value.
5. The Calculator User selects an operator such as addition, subtraction, multiplication, or division.
6. The Calculator visibly records the chosen operator in the expression line.
7. The Calculator User enters the next numeric value.
8. The Calculator updates the active expression and display.
9. The Calculator User selects the orange equals key.
10. The Calculator evaluates the entered expression.
11. The Calculator displays the result in the primary right-aligned result display and preserves the expression as context.
12. The Calculator User may continue calculating from the visible result, enter a new expression, or clear the calculation.

Flow 2 — Correct an Active Entry

1. The Calculator User is entering a calculation on the Calculator page.
2. The user notices an unwanted number or operator in the active expression.
3. The user selects the correction utility control.
4. The Calculator updates the active entry and visible expression to remove or revise the current input.
5. The user continues entering the intended number or operator sequence.
6. The user may evaluate the corrected expression or clear it.

Flow 3 — Clear a Calculation and Start Again

1. The Calculator User has an active entry, evaluated result, or error state on the Calculator page.
2. The user selects the clear utility control.
3. The Calculator removes the current calculation state.
4. The display returns to the ready state and indicates that the calculator is available for a new calculation.
5. The user enters a new calculation on the same page.

Flow 4 — Recover from an Invalid Calculation

1. The Calculator User enters an expression that cannot be evaluated, such as division by zero.
2. The user selects the equals key.
3. The Calculator identifies the expression as invalid and displays an error state instead of a numeric result.
4. The Calculator keeps correction and clear controls available.
5. The Calculator User either corrects the active expression or clears the calculation.
6. The Calculator returns to a usable entry or ready state.
7. The Calculator User continues with a valid calculation on the same page.

6. Visuals Colors and Theme

Muse: Dieter Rams
Headline: Less, but better arithmetic

venus-start must feel like a quiet, dependable physical instrument rather than a decorative application. The calculator itself is the complete visual hero: ordered, tactile, immediately comprehensible, and free of promotional content.

Color Tokens

• Blue and indigo accents are prohibited.
• Gradients are prohibited.
• The orange token is reserved for the equals control and active operator state.
• Amber is used sparingly for the status marker.

Typography

• Heading and label family: Archivo SemiBold.
• Body family: Archivo.
• Display numeral family: Archivo Medium with tabular figures.
• Page title: 28px.
• Primary result display: 72px.
• Key numerals: 18px.
• Standard labels: 12px.
• Micro-status and metadata: 10px.
• Uppercase labels use restrained 0.12em letter spacing.
• Display figures use tight tracking and no decorative treatment.
• Inter, Roboto, Arial, Helvetica, Open Sans, Lato, Poppins, and system-ui fonts are prohibited.

Shape and Surface Language

• Use a rectangular calculator chassis.
• Use a 2px charcoal perimeter around the calculator body.
• Use 1px charcoal internal rules.
• Use shallow 4px control radii.
• Use a subtle 3px hard lower shadow on the chassis only.
• Do not use soft cloud shadows, glassmorphism, floating cards, or hover-lift effects.
• Keys should read as machined controls within a unified ruled keypad panel.

Layout

• Present a full-viewport warm-grey workbench.
• Position one oversized calculator chassis slightly right of center on desktop.
• Target an approximate desktop object width of 760px.
• Use a narrow left rail for vertical wordmark and model metadata.
• Place a wide right-aligned display above the four-column keypad.
• On mobile, collapse left-rail metadata into a top rule.
• Keep the keypad edge-to-edge within safe margins on mobile.
• Do not add marketing headline sections, card grids, promotional CTAs, or multi-section landing content.

Imagery and Functional Detail

• Use no stock imagery, decorative illustration, emoji, or character artwork.
• The calculator is the sole product object.
• Fine diagrammatic marks, calibration ticks, a compact operation legend, and the dot-grid indicator may provide functional visual detail.
• The left rail must include VENUS—START, CALCULATOR 01, and READY.
• The display includes an amber status square at the far left.
• Operator keys show secondary labels: ADD, SUB, MULT, and DIV.

7. Signature Design Concept

The opening view is a full-viewport warm-grey workbench containing one oversized, slightly right-offset calculator chassis. A slim charcoal rail to its left carries vertical instrument metadata: VENUS—START, CALCULATOR 01, and READY.

The chassis uses a wide cream display band across its upper area. A small tabular expression line sits above a 72px, right-aligned live result. The amber status square at the left edge of the display provides the only secondary color cue. Below, a single ruled four-column keypad forms a cohesive mechanical panel: pale numeric keys, charcoal utility controls, clearly labeled operator keys, and a visually anchoring orange equals key at the lower right.

This concept recomposes only the accepted calculator content and controls. It introduces no marketing destination, supplemental workflow, or additional product behavior.

8. Interaction Model & Motion Direction

Interaction Model: Animated
Motion Tempo: restrained
Hero Dimensionality: flat

Landing Hero Motion Brief

• Focal subject: The oversized calculator chassis, specifically its cream display band, visible expression line, and orange equals key.
• Input → transformation → outcome thesis: A Calculator User presses a numeric, operator, utility, or equals key; the selected machined key darkens and depresses by 2px; the display updates to show the active entry, result, or recoverable error state.
• Motion vocabulary: Restrained mechanical feedback only. Keys return after 120ms. Display digits wipe from bottom to top over 80ms.
• Composed first frame: The warm-grey instrument field is visible immediately. The calculator chassis is static, slightly right of center, with the vertical metadata rail, amber status square, expression line, large result display, structured keypad, and orange equals key fully readable.
• Reduced-motion state: Remove the key return transition and digit wipe. Preserve immediate key contrast, static depressed-state confirmation while pressed, and an instantaneous readable display update.
• Prohibited movement: No parallax, floating, bouncing, elastic easing, particles, ambient animation, animated gradients, or decorative motion.

9. Non-Functional Requirements

NFR-01 — Single-Page Delivery

• Requirement: venus-start must be delivered as exactly one page, Calculator.
• Provenance: explicit.
• Rationale: The accepted product requirement specifies a simple single-page calculator design.
• Verification: Confirm that no additional first-party pages, modules, or navigational destinations are delivered.

NFR-02 — Simplicity and Scope Discipline

• Requirement: The calculator design and behavior must remain simple and limited to calculator interaction.
• Provenance: explicit.
• Rationale: Simplicity is an explicit product constraint.
• Verification: Confirm that the interface does not add unsupported features such as accounts, history, saved calculations, scientific functions, conversions, sharing, or promotional content.

NFR-03 — Legibility

• Requirement: The current expression, result, controls, and operation labels must be visually legible at a glance.
• Provenance: explicit design direction.
• Rationale: The product is intended to provide fast, dependable arithmetic through immediate comprehension and clear hierarchy.
• Verification: Confirm strong contrast between charcoal content and off-white surfaces, stable tabular display figures, visible operation labels, and unambiguous keypad grouping.

NFR-04 — Responsive Layout

• Requirement: The calculator must preserve its single-instrument layout across desktop and mobile form factors.
• Provenance: explicit design direction.
• Rationale: The desktop calculator spans approximately 760px, while mobile retains a usable keypad within safe margins.
• Verification: Confirm that desktop uses the offset chassis and metadata rail, while mobile collapses metadata into a top rule and keeps the keypad usable edge-to-edge within safe margins.

NFR-05 — Restrained Feedback

• Requirement: Interaction feedback must be immediate, mechanical, and restrained.
• Provenance: explicit design direction.
• Rationale: The intended tone is tactile and quietly dependable rather than decorative or app-like.
• Verification: Confirm 2px key depression, 120ms key return, 80ms display digit wipe, and the absence of prohibited decorative motion.

10. Tech Stack

• Frontend: React.
  [Default — not specified by user] React is sufficient for the single custom calculator page, keypad interactions, display state, and responsive presentation.

• Styling: CSS or CSS modules using project-specific design tokens.
  [Default — not specified by user] Styling must implement the specified palette, Archivo typography, ruled instrument layout, responsive behavior, and reduced-motion behavior.

• State management: Local client-side component state.
  [Default — not specified by user] The accepted calculator scope is anonymous and does not require persisted user-specific data, server-side state, or a backend API.

• Backend, storage, containers, and orchestration: Not required for the current scope.
  [Default — not specified by user] The calculator is a single public page with no account, history, persistence, provider integration, or external service requirement.

11. Assumptions and Constraints

Explicit Constraints

• The product is a simple calculator.
• The product is delivered as a single-page design.
• The Calculator is the entire product scope.
• Exactly one page is permitted: Calculator.
• No additional pages or modules may be added.
• The Calculator is publicly accessible with no identity requirement.
• The requested visual direction, palette, typography, surfaces, tone, and layout must be preserved.
• The generic indigo/blue-on-white SaaS template is forbidden.
• Decorative hero copy, marketing CTAs, and multi-section landing-page content are forbidden.
• Stock imagery, decorative illustration, character art, emoji, glassmorphism, gradient blobs, and soft floating-card styling are forbidden.

Required Inferences

• The calculator requires numeric entry, arithmetic operator selection, evaluation, result display, clearing, and correction to fulfill the accepted calculator purpose.
• Invalid calculations require a visible error state and a means to recover through correction or clearing.
• No identity, durable storage, account continuity, or differentiated permission model is needed because the accepted calculator interaction is anonymous and ephemeral.
• The calculator’s local time and memory-state indicators are visual instrument metadata only and do not establish saved memory or historical calculations.

Current Exclusions

The following are outside the current scope:

• Additional pages or routes.
• User registration, login, logout, profiles, or account management.
• Saved calculations, calculation history, exports, sharing, or collaboration.
• Memory operations or persisted memory values.
• Scientific, graphing, financial, conversion, or programmable calculator functions.
• Payment, subscription, analytics dashboards, notifications, or administrative interfaces.
• External provider integrations and external destinations.

12. Glossary

• Calculator: The sole public page and complete product interface for entering, evaluating, correcting, and clearing arithmetic calculations.
• Calculator User: The sole active human persona who uses the Calculator to obtain an arithmetic result.
• Expression: The visible sequence of entered numbers and arithmetic operators awaiting or retaining evaluation context.
• Result Display: The large, right-aligned primary display area showing the current numeric value or evaluated calculation result.
• Ready State: The calculator state in which it is available to receive a new calculation.
• Error State: A visible calculator state indicating that an expression cannot be evaluated, such as division by zero.
• Correction: A utility action that revises the current entered calculation.
• Clear: A utility action that removes the active calculation and returns the calculator to a ready state.