In my answer to the question about the LANL MANIAC I posted a picture of it in its natural habitat. In the picture there's a mystery device electrical-taped to one of the columns by the system console. Can anyone identify what it is and say why it would be found in a machine room?

MANIC I with object circled

Source: LANL via Flickr

Here's a perspective-corrected close-up:

Close up of device

The perspective correction makes it look deeper than it really is.

Estimated size: 30 cm (12") wide × 30 cm (12") high × ~4 cm (1½") deep

My best guess is that it's a hygrometer, perhaps to help keep the Williams tubes happy?

  • 5
    I'd guess hygrometer or similar, too. It was fairly common in later air-conditioned machine rooms for there to be a pen-recorder device monitoring temperature, humidity, &co.
    – dave
    Dec 3, 2021 at 12:48
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    @njuffa Here is a higher resolution version of the CHM image: icdn.digitaltrends.com/image/digitaltrends/…
    – jpa
    Dec 3, 2021 at 18:04
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    The similarity of the hole pattern to the paper tape reel visible at the table edge makes me wonder if it could be a backup tape. Perhaps some kind of system diagnostic program that was important to be always at hand but not easily lost :)
    – jpa
    Dec 3, 2021 at 18:28
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    the real question is how did the lady seated on the right button her shirt? Looks more complicated than the machine!
    – CCJ
    Dec 3, 2021 at 19:25
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    A lot of these comments seem to ignore the fact that the mystery object is strapped to a column with black electrical tape. A "tape winder?" A "tape cartridge?" Wouldn't those things be on a desk or on a shelf or in a drawer? "Strapped to a column, up high" sounds like something that the operators would want to look at from time to time. It doesn't look like any kind of clock, but "hygrometer" is starting to sound pretty believable. Dec 4, 2021 at 19:32

3 Answers 3


It's a thermometer, with a cover plate which doubled as an advertising placard removed.

Initial lead was this image:

A plastic advertising thermometer of same shape but roughly inverted colors as the sought-after model


(My reasoning being that due to lack of wires it wouldn't be any sort of chart recorder. I suspected it wasn't actually a bath scale because of the un-ergonomic platform. Additionally, most scales have a prominent/readable graticule for reading at more precision whereas this seemed designed more for a ballpark reading. This implied something more like humidity or rough temperature, but I couldn't find any vintage/modern hygrometers which rotated such a large disc.)

Throwing the above image into a Google reverse image search turns up this eBay listing https://www.ebay.com/itm/304494985260 which is an even closer match:

very similar device as above but with same color scheme as original MANIAC photos

The listing describes it as a "Wall Scale" but mentions:

portion where scale numbers are shown rotates around from 30 to 120, but rest at 80 mark.

and the pictures show the seller apparently twisting the dial itself with a finger, i.e. not indirectly applying a force to the so-called "scale" itself. So I suspect it is really a thermometer on some sort of bi-metallic spring.

Some of the other pictures in the listing shows the back side with an actual manufacturer stamp reading "Remembrance / B&B ST PAUL MINN. U.S.A.", and the mechanics of the back side again rule out it actually being a "scale". So despite the seller's description I do think it's a thermometer.

This leads to https://www.ebay.com/itm/114259942605 which claims of its artifact:


But its manufacturer nameplate mentions the patent number ultimately leading to https://patents.google.com/patent/USD162107S which is unambiguously a design patent for a "Thermometer":

Line drawing of device from its design patent

The 1950 filing date aligns nicely with the ca. 1953 date given on the https://www.computerhistory.org/revolution/supercomputers/10/28/46 picture.


Note: I'm answering my own question here. If someone can verify my findings in an answer I'll accept it.

Williams tubes (a.k.a. electrostatic cathode-ray storage tubes) were used for memory in the MANIAC Ia and the IAS machine on which it was basedb. These were small CRTs that stored bits as static electric charge on the front of the tube1. The addition of a thin metal sheet to the front of the tube allowed the stored values to be read2. Relying, as they did, on static electricity meant that they were very sensitive to environmental conditionsc, primarily humidity3. Too much humidity will prevent static charge from building up and too little humidity can cause excess charge build-up (or even arcing in high-voltage CRT circuitry). This was noted by a Princeton alumnus who remarkedd4:

The 40 CRTs (Williams Tube memory) had some strange characteristics. … [T]hey were very humidity-sensitive. On dry nights they would acquire “spurious bits” — 1s that should have been 0s.

A hygrometer in close proximity and similar conditions to the Williams tubes (i.e. two meters up between the console and the tubes) would thus be invaluable to the machine operators.

1 Omitting the sense plate from a Williams tube and connecting its input to another tube's input would allow the bits stored in that tube to be viewed by the operator. Two such display tubes can be seen in the photo at the left and right of the row of tubes. Here's a close-up (display on the left, storage on the right):

Close-up of Williams tubes

The actual tube is visible as the black and green square at the bottom of the device.

2 Put simply, if a write is done to a location on the tube then the voltage seen on the plate will differ depending on whether a 0 or 1 had previously been stored there. See the linked Wikipedia article for details of how this works.

3 Apparently vaguely close lightning strikes could also cause bit flipsc.

4 Earlier in their remark they misidentify the IAS machine as the very closely-related MANIAC. IMO this in no way detracts from their statement.

a Harlow, Francis H. and Metropolis, N., "Computing & Computers Weapons Simulation Leads to the Computer Era", LA-UR-83-5073, Los Alamos Science, LANL, Winter/Spring 1983

b "Electronic Computer Project", https://www.ias.edu/electronic-computer-project, retrieved 2021-12-03

c “The ­sensitivity of the memory, that was a big problem … If there was a storm with lightning, you would feel it in loss of bits. We spent many nights on the floor trying to tune it up.”
— Estrin, Gerald as quoted in "Daybreak of the Digital Age", https://paw.princeton.edu/article/daybreak-digital-age, retrieved 2021-12-03

d Clarkson, Bill, Comment in response to "Daybreak of the Digital Age", https://paw.princeton.edu/node/53751, retrieved 2021-12-03

  • 5
    Never seen a hygrometer like that, despite having them seen an used in may computing rooms of the 70s/80s. Back then they were usually pen recorders, as one want's to not only see random momentary values but record them. They were based on a clockwork driven cylinder and a operated of hair (Keratin reacts reliable to water) pulled by a spring for tension. This construction allowed the force needed for writing to be 90° to the force excreted by the hair/spring system.
    – Raffzahn
    Dec 3, 2021 at 13:58
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    Yea, it looks a little weird. Judging by the electrical tape it could be that one of the operators just went to the hardware store, picked up whatever hygrometer they had in stock, and stuck it up on the column. Dec 3, 2021 at 14:09
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    Whatever it is, it looks a lot like a bathroom scale with part of the lid ripped off, exposing the dial underneath. Dec 3, 2021 at 18:13
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    I think it is a chart recorder, but not a strip chart recorder. There were (probably still are) chart recorders that wrote on a rotating disk; the stylus moved like a phonograph arm. They could be electrically driven or clockwork. The chart record in the picture is not in use, because it has no paper on it. Instead you can see the bare disc that would hold the paper when it is in use. Dec 3, 2021 at 21:07
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    @WayneConrad, OK, maaaaaaaybe a chart recorder, but I question whether it's thick enough to house the clockwork that would rotate the disk. Also, the fuzzy, red blobs that I see through the upper window look like they could be stylized, big-font, display numbers. I'm subscribing to the (non-recording) hygrometer theory. Dec 4, 2021 at 19:36

The large and the small holes, could be a clue, maybe like for a sensor ( some type of optical or chemical sensor ), testing something at one level and then at another, unless they're something to do with ink.

Those holes in the unknown device, are a lot like the paper-tape-reel, however, the wheel of the unknown device extends a lot further out past the holes, than the paper-tape-reel. And, I'm not sure the spacing between the small and round holes in the unknown device is the same as on the paper-tape-reel.

It looks difficult to fit lasting batteries in there, more like a clockwork powered device.

Adding -

  • Electrical conductivity ( electrical resistance ) of air reader, possibly relevant to the memory technology used
  • Ozone reader, they existed well before
  • Unlikely, some type of hydrogen chemical reader

The following is a type of guess -

A modified kitchen scale -

  • Modified to move the wheel slowly, clicking between the small and round holes
  • And, not visible, out of frame of the picture, could be some type of light-emitter, and / or, a light-sensor, with either or both the light-emitter and the light-sensor being focused on only one of the holes, by using a small-telescope or telescopic-lens etc. The small holes containing a different reflector or filter than the large holes. The large air-gap between the visible half of the unknown-device and the possible other half which is not in the picture, could of made it easier to detect differences in the air with the sensors they had back then, rather than a small gap. ( Maybe, sensors or light-emitters etc., could also be focused on distant points by by putting them in hollow tubes or reflective parabolic-dishes like searchlights / flashlights ).

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