RPN Calculator

Purpose & User Intent:
This tool provides an online HP calculator emulator that concentrates on Hewlett-Packard style calculations. It serves students, engineers, and finance professionals who require authentic HP workflows (RPN, financial functions) in a browser. The goal is to deliver precise, repeatable results with stack-based behavior and mode fidelity that mirrors common HP devices. Users perform routine algebra, scientific calculations, and financial tasks without software installation, while preserving familiar keyboard semantics for speed and accuracy.

Core Logic & Features:
Required: RPN stack operations, mode switching (Scientific/Financial/RPN), basic arithmetic, financial functions (PMT, NPV, IRR), and memory/register support. Optional/Advanced: algebraic entry as a convenience layer, calculation history, and export of results. The tool emphasizes correctness, deterministic results, and reproducible workflows, not a full device clone.

Inputs & Outputs:
Inputs include mode (required), operands (numeric, with units where applicable), and function parameters (interest rate, periods, cash flows). Outputs return a numeric result, optional formatted display (scientific/decimal), and an optional per-field error signal. Precision presets adjust decimal places with consistent rounding rules.

Algorithms & Calculations:
RPN uses a stack data structure; operations pop required operands and push results. Financial functions emulate standard formulas: PMT = r*(1+r)^n/((1+r)^n-1); NPV = sum CF_t/(1+i)^t; IRR found via iterative methods. Edge cases, such as division by zero, negative periods, or invalid rates, are handled with explicit error flags.

Error & Edge Cases:
Invalid inputs trigger input-level validation (type, range, required fields). Division by zero, negative periods for time-based functions, or missing cash flows raise controlled errors. External data is not required; calculations remain in-browser.

Industry/Region & Localization:
Supports locale-aware decimal separators and currency-friendly formatting. Currency, rate conventions, and date conventions can align with user locale; no outside data is assumed unless provided.

Assumptions & Exclusions:
Assumes users intend HP-style workflows and does not claim exact replication of any specific model. Graphing, unit testing, and offline installation are out of scope. The tool focuses on core HP calculator capabilities relevant to education and professional use.