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Getting Started

First-time walkthrough of the 3-Way Calculator.

This guide walks you through your first calculation.

The three fields

The calculator screen shows three values:

Field Meaning (additive) Meaning (subtractive) Example
Before X% Price before tax Original amount before deduction $100.00
After X% Price including tax Remaining amount after deduction $115.00 / $85.00
X% Amount The tax amount The deduction amount $15.00

The X is replaced by the current rate (e.g., “Before 15%”). The relationship depends on the calculation direction:

  • Additive (+): After = Before + Amount
  • Subtractive (−): After = Before − Amount

You can toggle between the two modes using the + / − button on the toolbar.

How focus works

Tap any field to make it the active field (highlighted with a coloured border). The active field is the “anchor” — you type into it, and the other two fields recalculate automatically using the current flat rate and direction.

Example: If you tap After and enter 115.00, the calculator automatically computes:

  • Before = 100.00
  • Amount = 15.00 (at the default 15% rate)

If you then tap Before and enter 200.00, the calculator switches anchor:

  • After = 230.00
  • Amount = 30.00 (still at 15%)

Entering numbers

Use the on-screen keypad to type numbers. It works like a standard calculator:

Button Action
0–9 Enter digits
. Decimal point (only one allowed per value)
⌫ Backspace — delete the last character
C Clear — reset all three fields to zero

Values are limited to 12 integer digits. The number of decimal places is configurable in Settings (0, 1, 2, or 3); 2 decimal places is the default.

What you see

  • The active field has a highlighted border
  • Inactive fields show the computed values
  • Values are formatted with thousands separators (e.g., 1,234.56)
  • If an error occurs, a message appears between the toolbar and the keypad

Try it now

  1. The calculator should be at After, 0.00.
  2. Tap the After field if it isn’t already highlighted.
  3. Press 1, 0, 0 on the keypad — After shows 100.00.
  4. Watch Before and Amount update automatically.
  5. Now tap Before and enter a different number — the other two fields update.

Next steps