Register to reply

'comptometer'- a mechanical adder

by Andy Resnick
Tags: adder, comptometer, mechanical
Share this thread:
Andy Resnick
Dec23-10, 10:41 AM
Sci Advisor
P: 5,539
Here's a small selection of images I've been working on for the past couple of weeks. The object is a 'comptometer'- a mechanical adder. Mine was given to me by a friend who rescued it from his fabric factory- it's a 1940's model. It mostly works, but there's no way I am skilled enough to take it apart and clean it. I decided I liked the steampunk look of it, and at high magnification you can see all the fibers that floated inside the casing over the decades.

These are easily the most difficult images I have ever taken- each shot took the better part of a day to set up. Not only was I working with difficult lenses- the Luminar zoom (see, Andre? I *do* use a zoom:) ) and 100mm Luminar- I was also using the lenses way outside of their design limits- working distances 3x -10x normal, stopped down to near pinholes to get a decent depth of focus, and I needed 4 or 5 fiber lights to get the illumination even or directed where I needed it.

The images of the whole device were taken with a 24mm macro, and most of the other images were taken with either the zoom, 100mm, or 63mm Luminars- there's a couple near the end taken with the 25mm. Since the mechanism is buried inside the frame, there was no point to using the 16mm. After the over-all views, there's an image of the bottom where the keys are anchored and held in place with a hairspring mechanism, an image of the front mechanism and dial wheels, a couple 'architectural' views, and then high-magnification shots of parts of the mechanism

I'll be posting the full images on my blog, so here's a taste:

Call this my Christmas present to fellow PF photographers :)
Phys.Org News Partner Science news on
'Smart material' chin strap harvests energy from chewing
King Richard III died painfully on battlefield
Capturing ancient Maya sites from both a rat's and a 'bat's eye view'
Dec23-10, 12:45 PM
PF Gold
edward's Avatar
P: 882
Great Pics Andy. My older sister used to operate a comptometer when she was an accountant for North Electric Company back in the late fifties. Untill now I had never seen inside of one.

The Felt & Tarrant Manufacturing Company built both comptometers and comptographs
Yours is definitely an original.
Andy Resnick
Dec23-10, 02:55 PM
Sci Advisor
P: 5,539
Thanks! Yeah, it's a 'Model M':

And originally, I was hoping to really get at the mechanism, like what this guy can do:

but I don't that kind of time or skill.

Dec23-10, 07:39 PM
lisab's Avatar
P: 3,008
'comptometer'- a mechanical adder

Those are fabulous, Andy, thanks so much!

I'm afraid all I got you for Christmas was a smiley...
Dec24-10, 07:51 AM
Andre's Avatar
P: 5,460
Very nice work indeed, Andy, thanks for sharing.
Dec29-10, 03:44 PM
PF Gold
fuzzyfelt's Avatar
P: 742
Great, thanks, Andy! Seasons Greetings and Happy New Year!

Register to reply