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The Calculator is a FORTH-programmable scientific RPN (Reverse Polish Notation) calculator based on the IVT (IVEE-TINY) engine by zooxo/deetee.

What is RPN?

In RPN, operands are entered before the operator. Instead of 3 + 4, you enter 3, then 4, then +. Numbers are pushed onto a stack; operations consume values from the top of the stack and push the result.

• D (DUP) pushes/duplicates the current number onto the stack, or confirms number entry.
• C (DROP) removes the top of stack, or clears the current number entry.

Keyboard Layout

The keypad has two modes. Press F to toggle the shifted layer.

Normal mode

Col 1	Col 2	Col 3	Col 4
F (shift)	7	8	9
E (10^x)	4	5	6
N (negate)	1	2	3
C (DROP/clear)	0	. (decimal)	D (DUP/enter)

F-shifted mode (press F first)

Col 1	Col 2	Col 3	Col 4
MENU	SUM+	PRG	/
SWAP	DICT	USR	*
ROT	RCL	STO	-
CA	PI	INT	+

Key Reference

Key	Description
0–9, .	Enter digits and decimal point
E	Scientific notation exponent (Y × 10^X)
N	Negate (change sign)
D	DUP — duplicate top of stack / confirm number entry
C	DROP — remove top of stack / clear current entry
F	Shift to function layer; double-press opens user MENU
+ − × ÷	Basic arithmetic
SWAP	Swap top two stack values (1 2 → 2 1)
ROT	Rotate stack (1 2 3 → 2 3 1)
STO / RCL	Store/recall a number to memory slot 0–9 (enter slot number first)
CA	Clear all — clears stack and statistics memories
PI	Push π onto the stack
INT	Integer part of top value
SUM+	Add X (or X,Y) data point for statistics / linear regression
DICT	Browse the full dictionary of all commands
USR	Assign a dictionary entry to the user menu
MENU	Open the user-defined menu
PRG	Edit a user program (enter program number 0–15 first)

Dictionary Functions

Access all commands via DICT (F+4). Functions include:

Math: SQRT, POW (y^x), INV (1/x), EXP, LN, SIN, COS, TAN, ASIN, ACOS, ATAN, GAMMA (ln Γ)

Stack: DUP, DROP, SWAP, ROT, OVER

Statistics: SUM+, SUMclr, MEAN/STDEV, LR (linear regression)

Other: PV (present value), ND (normal distribution PDF/CDF), P>R / R>P (polar/rectangular), nPr, nCr, SOLVE (root finder)

Control flow (for programs): IF, ELSE, THEN, BEGIN, UNTIL, <, =, <>, >

Programming

IVT supports up to 16 user programs (numbered 00–15) with up to 440 total steps.

To edit a program:

1. Enter the program number (e.g. 0, 5)
2. Press F + PRG
3. Navigate steps with E (up) and N (down)
4. Insert steps by pressing a key or selecting from DICT
5. Delete a step with .
6. Save and exit with C

Note

User program 00 is reserved for the SOLVE (root finder) function.

Limits

Item	Limit
Stack depth	24
Significant digits	7
Memory slots (STO/RCL)	10 (0–9)
User programs	16
Total program steps	440
User menu slots	32
Number precision	IEEE 754 32-bit float (~6–7 decimal digits)

Example Programs

ABS:    DUP 0 > IF THEN NEG
SINH:   EXP DUP INV NEG + 2 /
LOG:    LN 1 0 LN /
%:      OVER / 1 0 0 *
C<>F:   DUP 1 . 8 * 3 2 + SWAP 3 2 - 1 . 8 /