Spotlight: Casio Mini CM-605
Quick Facts
Model: CM-605
Company: Casio
Type: Four Function
Power: 4 x AA
Case: Leather Case
Memory: No memory registers
Years in Production: Starting in 1974
Display: 6 digits
Operating Mode: Chain
Shout out to Monrovia Vintage in Monrovia, California.
A Display of Six Digits (with a Surprise)
The Casio Mini (CM-605) is a vintage calculator from 1974. The calculator has the four arithmetic functions (+, -, ×, ÷). Operations are carried out as they are entered.
The zeroes in the CM-605 are shown as small zeroes. Hence, 4000 would be shown as 4ooo.
One limitation is that we can only enter numbers up to six digits. If the number is less than 1, we can only enter 5 digits after the decimal point as the leading zero is inserted automatically.
But there is a secret. It turns out that Hewlett Packard isn’t the only one to have calculators with a SHOW function. This CM-605 has a show key, [ ►], when held, it will show up to six additional digits.
From the short time that I have worked with the CM-605:
* Integers and integer parts can be shown up to 12 significant digits.
* Fractional parts can be shown up to six significant digits.
I think I can best show the power of the show key [ ► ] by a few examples:
4 ÷ 7 ≈ 0.571428
Keystrokes: [ AC ] 4 [ ÷ ] 7 [ = ]
Display: o.57142 hold [ ► ] 8ooooo
4329 × 9277 = 40160133
Keystrokes: [ AC ] 4329 [ × ] 9277 [ = ]
Display: 4o16o1 hold [ ► ] 33.oooo
5.7 ÷ 4.95 ≈ 1.15151
Keystrokes: [ AC ] 5.7 [ ÷ ] 4.95 [ = ]
Display: 1.15151 hold [ ►] oooooo
0.975 × 6.37 ÷ 8 ≈ 0.776343
Keystrokes: [ AC ] 0.975 [ × ] 6.37 [ ÷ ] 8 [ = ]
Display: o.77634 hold [ ► ] 3ooooo
Because there is no square root function, here are some mathematical constants to five digits:
ln 2 ≈ 0.69315
π ≈ 3.14159
e ≈ 2.71828
√2 ≈ 1.41421
√3 ≈ 1.73205
√5 ≈ 2.23607
Final Thoughts
I love collecting calculators made in the 1970s, especially with classic LED digits. The six-display with the show button is unique for Casio calculators. This calculator is a great showpiece.
Source
“CASIO MINI-CM-605 (A)” Casio Ledudu. June 15, 2011. https://casio.ledudu.com/pockets.asp?type=872&lg=eng Retrieved March 31, 2026.
Eddie
All original content copyright, © 2011-2026. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.
