MB 89F is a standard calculator that works in exact fractions — every value is kept as a whole-number numerator over a whole-number denominator, so the math never drifts. You key a calculation the natural way and press equals. It has mixed-number entry, tape-measure rounding (1/8 to 1/64), fraction ↔ decimal conversion, unit tagging and conversion (IN / FT / MM / MT), and a built-in user manual and cheat sheet.
Tap the gear icon (top-right) to open Settings, then choose User Manual for a full walkthrough or Cheat Sheet for a quick key reference. Most questions are answered there.
How do I enter a fraction?
Use the b/c key: press 3 b/c 4 for
3/4. For a mixed number, use SPC for the gap: 2 SPC
1 b/c 2 gives 2 1/2.
How do I do a calculation?
Just like a normal calculator. Key a number, press an operator, key the next number,
then press =. Example: 3 b/c 4
+ 1 b/c 2 = shows
1 1/4. Operations chain left to right, and pressing = again repeats the
last operation.
What do the gold Φ and blue Γ keys do?
They are shift keys. Φ reaches the gold labels (mode, decimal places,
fraction/decimal conversion, store to memory, clear-all). Γ reaches the
blue labels (1/x, x², ½x to find a centerline, 2x to double, and recall from memory).
Square root has its own √x key.
How do I round to a tape-measure fraction?
Press 1/8, 1/16, 1/32, or 1/64 to
round the displayed value to that increment. Press TRU to restore the exact
original value.
How do I convert between inches and millimeters?
Tag a value by tapping IN, FT, MM, or
MT. Then tap a different unit key to convert to it exactly.
Still stuck, found a bug, or have a suggestion? Email baymanpllc@gmail.com and I'll get back to you.