# Fathometer Question **URL:** \ **Category:** Factual Questions\ **Created:** [February 2, 2019, 1:07am UTC](https://boards.straightdope.com/t/fathometer-question/828816 "2019-02-02T01:07:18Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![SanDiegoTim](https://avatars.discourse-cdn.com/v4/letter/s/85e7bf/32.png) [@SanDiegoTim](https://boards.straightdope.com/u/SanDiegoTim)\ **Post date:** [February 2, 2019, 1:07am UTC](https://boards.straightdope.com/t/fathometer-question/828816/1 "2019-02-02T01:07:18Z")
How long would it take a “ping” (that might not be the correct terminology) to return to a Fathometer atop the Mariana Trench (36,000’)? ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [February 2, 2019, 1:25am UTC](https://boards.straightdope.com/t/fathometer-question/828816/2 "2019-02-02T01:25:29Z")
[This Wikipedia article](https://en.wikipedia.org/wiki/Speed_of_sound#Water) has a graph of the speed of sound vs. depth in the ocean. I think you’d have to perform some numerical integration to get an exact answer, but taking a rough average of 1520 m/s, it would take about 14.4 seconds to reach the sea floor and return. ---
**Author:** ![digs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/digs/32/14889_2.png) [@digs](https://boards.straightdope.com/u/digs)\ **Post date:** [February 2, 2019, 1:30am UTC](https://boards.straightdope.com/t/fathometer-question/828816/3 "2019-02-02T01:30:18Z")
I’m amused by the word “Fathometer”. Would that make my tape measure an “Inch-o-meter”? (Well, it is now!) Oh! The ruler I bought in Paris can be a “Millimetermeter”… ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 2, 2019, 1:41am UTC](https://boards.straightdope.com/t/fathometer-question/828816/4 "2019-02-02T01:41:40Z")
> [@digs](#): > > I’m amused by the word “Fathometer”. Would that make my tape measure an “Inch-o-meter”? (Well, it is now!) > > Oh! The ruler I bought in Paris can be a “Millimetermeter”… There’s also mileometer (or is that not used in the U.S.?) And barometer - although that’s probably cheating, it just comes from the same root as the unit of pressure. ---
**Author:** ![Littleman](https://avatars.discourse-cdn.com/v4/letter/l/ccd318/32.png) [@Littleman](https://boards.straightdope.com/u/Littleman)\ **Post date:** [February 2, 2019, 1:52am UTC](https://boards.straightdope.com/t/fathometer-question/828816/5 "2019-02-02T01:52:43Z")
Speed o meter Though it’s not pronounced that way currently. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 2, 2019, 2:03am UTC](https://boards.straightdope.com/t/fathometer-question/828816/6 "2019-02-02T02:03:28Z")
> [@Littleman](#): > > Speed o meter > > Though it’s not pronounced that way currently. Speed is not a unit. There are hundreds of words xxx-meter where xxx is the thing being measured. The unusual thing is that fathom is a _unit_ of depth. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 2, 2019, 2:07am UTC](https://boards.straightdope.com/t/fathometer-question/828816/7 "2019-02-02T02:07:52Z")
Aside from mileometer (which may only be British), the only similar ones I can come up with are calorimeter, coulometer and ammeter. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [February 2, 2019, 2:52am UTC](https://boards.straightdope.com/t/fathometer-question/828816/8 "2019-02-02T02:52:42Z")
I’m pretty sure mileometer is only British. The US term of course is odometer. But why isn’t it spelled mileometre? ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 2, 2019, 3:14am UTC](https://boards.straightdope.com/t/fathometer-question/828816/9 "2019-02-02T03:14:42Z")
> [@markn\_1](#): > > But why isn’t it spelled mileometre? I’m not sure if you’re joking, but this sense of meter (measuring instrument) has the same spelling in British English. ---
**Author:** ![Littleman](https://avatars.discourse-cdn.com/v4/letter/l/ccd318/32.png) [@Littleman](https://boards.straightdope.com/u/Littleman)\ **Post date:** [February 2, 2019, 3:19am UTC](https://boards.straightdope.com/t/fathometer-question/828816/10 "2019-02-02T03:19:31Z")
> [@Riemann](#): > > Speed is not a unit. There are hundreds of words xxx-meter where xxx is the thing being measured. The unusual thing is that fathom is a _unit_ of depth. So…? I was just pointing out it was another amusing use of the xxx-o-meter form. What would imply I was saying speed was a unit of measure? ---
**Author:** ![Littleman](https://avatars.discourse-cdn.com/v4/letter/l/ccd318/32.png) [@Littleman](https://boards.straightdope.com/u/Littleman)\ **Post date:** [February 2, 2019, 4:16am UTC](https://boards.straightdope.com/t/fathometer-question/828816/11 "2019-02-02T04:16:11Z")
Wait is speedometer not used in UK or something? ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 2, 2019, 4:38am UTC](https://boards.straightdope.com/t/fathometer-question/828816/12 "2019-02-02T04:38:57Z")
> [@Littleman](#): > > So…? > > I was just pointing out it was another amusing use of the xxx-o-meter form. > > What would imply I was saying speed was a unit of measure? What **digs** noted and found amusing was clearly the use of a unit of measurement with meter, so your post was a _non sequitur_. If you want to insist that you actually understood that, and you were deliberately broadening the discussion to include all vaguely amusing words that end in meter, well I can’t refute that. But I’m not really sure what you find amusing about the word speedometer. Sphygmomanometer might be more likely to elicit a chuckle. ---
**Author:** ![Littleman](https://avatars.discourse-cdn.com/v4/letter/l/ccd318/32.png) [@Littleman](https://boards.straightdope.com/u/Littleman)\ **Post date:** [February 2, 2019, 5:06am UTC](https://boards.straightdope.com/t/fathometer-question/828816/13 "2019-02-02T05:06:05Z")
Maybe that it’s not a unit of measure and goes along lines of all the old hokey items that used to just add o meter to everything yet is used all the time like it’s normal. Eager to argue for no apparent reason much? ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 2, 2019, 5:15am UTC](https://boards.straightdope.com/t/fathometer-question/828816/14 "2019-02-02T05:15:21Z")
> [@Littleman](#): > > Maybe that it’s not a unit of measure and goes along lines of all the old hokey items that used to just add o meter to everything yet is used all the time like it’s normal. Maybe. ---
**Author:** ![Deflagration](https://avatars.discourse-cdn.com/v4/letter/d/3ab097/32.png) [@Deflagration](https://boards.straightdope.com/u/Deflagration)\ **Post date:** [February 2, 2019, 10:34am UTC](https://boards.straightdope.com/t/fathometer-question/828816/15 "2019-02-02T10:34:01Z")
And amusingly a [Gas Holder](https://en.wikipedia.org/wiki/Gas_holder) (that’s Gas as in Natural Gas not Gas as in Gasoline) is called a Gasometer. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 2, 2019, 1:53pm UTC](https://boards.straightdope.com/t/fathometer-question/828816/16 "2019-02-02T13:53:16Z")
And a voltmeter measures electric potential, while (for some reason) a potentiometer doesn’t measure anything, being an input device rather than an output device. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [February 2, 2019, 2:51pm UTC](https://boards.straightdope.com/t/fathometer-question/828816/17 "2019-02-02T14:51:59Z")
> [@Chronos](#): > > And a voltmeter measures electric potential, while (for some reason) a potentiometer doesn’t measure anything, being an input device rather than an output device. I’m thinking a potentiometer is called that because it _can_ be used to measure electrical potential, i.e., voltage, unlike a plain rheostat. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 2, 2019, 2:54pm UTC](https://boards.straightdope.com/t/fathometer-question/828816/18 "2019-02-02T14:54:36Z")
> [@Deflagration](#): > > And amusingly a [Gas Holder](https://en.wikipedia.org/wiki/Gas_holder) (that’s Gas as in Natural Gas not Gas as in Gasoline) is called a Gasometer. Interesting that you pointed this out. I grew up with “gasometer” (they were common in the U.K. when I was a kid), and I vaguely assumed that it must come from some other archaic sense of “meter”. But I just learned that it’s because the design derives from an actual measuring instrument invented by Lavoiser. > **[Gas holder | Etymology](https://en.wikipedia.org/wiki/Gas_holder#Etymology)** > > Antoine Lavoisier devised the first gas holder, which he called a gazomètre, to assist his work in pneumatic chemistry. It enabled him to weigh the gas in a pneumatic trough with the precision he required. He published his Traité Élémentaire de Chimie in 1789. James Watt Junior collaborated with Thomas Beddoes in constructing the pneumatic apparatus, a short-lived piece of medical equipment that incorporated a gazomètre. Watt then adapted the gazomètre for coal gas storage. > The anglicisation "ga... ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 2, 2019, 2:59pm UTC](https://boards.straightdope.com/t/fathometer-question/828816/19 "2019-02-02T14:59:54Z")
> [@DPRK](#): > > I’m thinking a potentiometer is called that because it _can_ be used to measure electrical potential, i.e., voltage, unlike a plain rheostat. So it can _potentially_ be used to measure potential, a potentiopotentiometer? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 2, 2019, 11:14pm UTC](https://boards.straightdope.com/t/fathometer-question/828816/20 "2019-02-02T23:14:51Z")
I think the idea is that you use a potentiometer as one component of a Wheatstone bridge or similar setup, and then use that entire circuit to measure voltage.