Payas Reckoner

Overview

Payas Reckoner is a fully client-side, multi-mode calculator application that runs entirely in your browser — no server, no build step, no installation. Open index.html and start calculating.

It follows the Payas Design System and includes 10 distinct calculator modes, all with dark/light theme support and full keyboard navigation.

Property	Value
Stack	HTML5 · CSS3 · Vanilla JavaScript ES2022
Styling	Bootstrap 5.3.3 (grid/utilities only)
Icons	Material Icons (Google)
Persistence	localStorage + Markdown file export
Charts	HTML5 Canvas (custom engine, no library)
License	GNU General Public License v2.0
Browser support	Chromium-based · Firefox
Responsive	Desktop · Tablet · Mobile (≥320px)

Quick Start

No build or server needed:

# Option 1 — open directly
xdg-open index.html          # Linux
open index.html              # macOS
start index.html             # Windows

# Option 2 — serve locally (recommended for currency fetch)
python3 -m http.server 8080
# Then visit http://localhost:8080/payas-reckoner/

Calculator Modes

#	Mode	Description
1	Basic	Standard 4-operation calculator with memory (MC/MR/M+/M−/MS) and history
2	Scientific	Trig, hyperbolic, logarithms, complex entry, angle modes (DEG/RAD/GRAD)
3	Graphing	Canvas-based function plotter with pan/zoom, 5 traces, regression overlay
4	Financial	TVM, NPV/IRR, amortization schedule, bond pricing
5	Programmable	Custom interpreter (LET/FOR/WHILE/IF/PRINT/INPUT), step debugger, save/load
6	RPN	HP-style reverse Polish notation with 4-level stack, UNDO, full scientific ops
7	Statistical	Descriptive stats, regression, normal/binomial/Poisson distributions, t-test
8	Unit/Currency	12 unit categories, live currency rates, favourites, custom units
9	Programmer	BIN/OCT/DEC/HEX, bitwise ops, interactive 64-bit grid, two’s complement
10	Matrix	Up to 8×8 matrices, det, inv, RREF, LU/QR, eigenvalues, cofactor/adjugate

Features

Dark / Light theme — toggle with Ctrl+D or the toolbar button, persisted to localStorage
Calculation history — last 100 entries, toggle with Ctrl+H, exportable to .md
Keyboard shortcuts — full keyboard support in every mode
Responsive — mobile (≥320px), tablet, desktop
No external JS frameworks — vanilla JavaScript + Bootstrap CSS only
Offline-capable — all modules load without a server; currency rates cached in localStorage

Keyboard Shortcuts

Shortcut	Action
0–9, .	Number entry
+ - * /	Basic operators
Enter / =	Calculate / push (RPN)
Escape	Clear / AC
Backspace	Delete last character
Ctrl+Z	Undo (where supported)
Ctrl+H	Toggle history panel
Ctrl+M	Open mode drawer
Ctrl+D	Toggle dark/light theme
F1	Open documentation
Tab	Next input field

Project Structure

payas-reckoner/
├── index.html
├── assets/
│   ├── css/
│   │   ├── payas-theme.css
│   │   └── calculator.css
│   └── js/
│       ├── app.js
│       ├── calculators/
│       │   ├── basic.js
│       │   ├── scientific.js
│       │   ├── graphing.js
│       │   ├── financial.js
│       │   ├── programmable.js
│       │   ├── rpn.js
│       │   ├── statistical.js
│       │   ├── unit-conversion.js
│       │   ├── programmer.js
│       │   └── matrix.js
│       └── utils/
│           ├── math-engine.js
│           ├── storage.js
│           └── exporter.js
├── data/
│   ├── history.md
│   ├── memory.md
│   ├── programs.md
│   └── custom-units.md
├── docs/
│   └── documentation.md
├── LICENSE
└── README.md

Get Payas Reckoner

Resource	Link
GitLab Repository	gitlab.com/samanscode/payas-reckoner
Download ZIP	payas-reckoner-main.zip