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Ever wish there was an easy way to quickly convert from one unit of measurement to another? Sure, today you can whip out your handy phone/calculator/camera/flashlight/etc. and do a quick calculation, but that level of technology has not always been available. Instead, there were really clever cardboard converter tools. Unlike a nomograph (where the numbers stay still and you move a straight edge over the page to find your answers), these sliding converters let you slide the numbers around inside a frame to get what you needed. We have several examples here, courtesy of Paul!
Calendar Calculator from Presidio (New for November 2022)
Amplifier Design Calculator from Anzac
OKI Electronics Measurement Converter
Hughes Microwave Calculator
Hughes Millimeter Wave System Calculator
M/A-COM VSWR Calculator
Screw and Thread Sizes from Lufkin Tools
Calendar Calculator from Presidio
Ok, to be honest, we don't know what this thing is actually called, but the idea is that you can figure out what day is exactly x days from any other day. For example, if you point the little arrow to a day (in the graphic, it's pointing to November 4th), then you can easily tell which day is exactly 90 days away (turns out to be Feburary 2nd). Or 180, or whatever. You can also work it backwards. If, for example, your birthday is on January 31st and you need begin retirment paperwork 180 days in advance, you just set the "180" line to your birthday and look to see where the arrow lands (hint: it's August 4th). Very handy!!
Amplifier Design Calculator from Anzac
New for August 2022. Now, we're not saying the Unknown Editor is old school or anything, but he did have a few of these old school tools in his personal collection! This one is from Anzac, formerly a division of Adams-Russell, which eventually became part of M/ACOM. It's an Amplifier Design tool that helps you calculate cascade noise figure, cascade 3rd order IM intercept, 3rd order intercept, and 3rd order spurious-free dynamic range. That's a lot for one little bit of cardboard!
OKI Electronics of America Measurement Converter
Here's an example of the frame of a "Measurement Converter" from OKI Electronics of America, followed by an inside look at the inside piece (the bit that slides around).
Here's what it looks like when you put them together.
So how does it work? Say, for example, you get a measurement that for whatever reason shows up in rods (well, it's better than cubits). Simply slide the inside piece until "Rod" has a one next to it, and voila! All the conversion factors are listed right there.
Kind of simplistic, sure, but handy nonetheless.
Microwave Calculator from Hughes (1988)
Some of these old slide charts had much more complex numbers on them...like this one from Huges Aircraft Company.
They made one for millimeter waves, too (1975)!
VSWR Calculator from M/A-COM (1983)
Screw and Thread sizes from Lufkin Tools, 1935
Thank you to Paul for the generous loan of all of these converters!