Arithmetic Operations

The calculator has a full four-function arithmetic engine built into the keypad. You can perform calculations on the active field just like a standard calculator.

Basic arithmetic

The four basic operators work as you would expect:

Button	Operator	Example	Result
+	Add	100 + 50 =	150.00
−	Subtract	100 − 50 =	50.00
×	Multiply	100 × 3 =	300.00
÷	Divide	100 ÷ 3 =	33.33

How chain calculations work

1. Enter a value on the active field.
2. Press an operator (+, −, ×, ÷).
3. Enter a second value.
4. Press = to compute the result.

The result replaces the value on the active field. The other two fields (Before/After/Amount) are then recalculated based on this new value.

Example: You want to add a service charge of 50.00 to a Before price of 200.00.

1. Tap the Before field.
2. Enter 200.
3. Press +.
4. Enter 50.
5. Press =. Before becomes 250.00. After and Amount recalculate at the current rate.

If you want to start a new calculation, just begin entering a new value — the previous operation is cleared.

The % (percent) key

The percent key has two different behaviors depending on the context:

Mode 1: Chain calculation (with a pending operator)

When used after an operator, % computes a percentage of the first operand.

Example: Add 10% to 100

1. Enter 100.
2. Press +.
3. Enter 10.
4. Press %.

The calculator computes: 100 + (100 × 10%) = 100 + 10 = 110

This is equivalent to “100 plus 10 percent of 100” — the standard way percentages work on most calculators.

Mode 2: Standalone percent calculation (no pending operator)

When pressed without a pending operation, % calculates the Amount for the current field using the current flat rate.

On the After field: Amount = After × rate

Example: After = 100, rate = 15% → Press % → Amount = 15, After stays 100, Before = 85

On the Before field: Amount = Before × rate

Example: Before = 100, rate = 15% → Press % → Amount = 15, Before stays 100, After = 115

On the Amount field: Amount / 100 — converts the displayed percentage to a decimal.

Example: Amount field shows 15 → Press % → Amount becomes 0.15

Clearing

Button	Action
C (Clear)	Resets all three fields to zero, clears any pending operation, and removes error messages
⌫ (Backspace)	Deletes the last character from the active field only

After pressing C, the calculator is in a clean state — all values are 0.00 and no operation is pending.

The keyboard Escape key is equivalent to C. The Backspace key works like ⌫.

Division by zero

If you attempt to divide by zero, the calculator shows:

Error: Division by zero

Press C or Escape to clear the error and start again.

Limit exceeded

If a calculation produces a value exceeding 999,999,999,999.99 (~1 trillion), the calculator shows:

Error: Limit Exceeded

Reduce your input values or the rate, then press C or Escape to continue.

Practical examples

Apply a discount

You can apply a percentage discount using arithmetic:

1. Enter the original price (e.g., 200.00).
2. Press −.
3. Enter the discount percentage (e.g., 15).
4. Press %.
5. Press =. The discounted price replaces the original.

For a more intuitive approach, use subtractive mode — see Use case 8: Apply a discount for step-by-step instructions.

Calculate a markup

1. Enter the cost price.
2. Press +.
3. Enter the markup percentage.
4. Press %.
5. Press =. The marked-up price appears.

Split into multiple operations

You can chain more than two values:

1. Enter 100.
2. Press +.
3. Enter 50.
4. Press +. (This computes 100 + 50 = 150 and stores it.)
5. Enter 25.
6. Press =. Result: 175.00.