first time you were amazed by metrology/precision/stability/resolution?

[coppercone2]

My first 'oh shit' moment was when I made a precision RTD interface and I could pick up the touch of my finger on a metal vise and actually do a 'thermal PWM' by tapping the vice and watching the temperature go by like 0.002c.

The second big one was buying a electrometer and seeing the readings changed when I touched my head from several feet away.

[AndyC_772]

Every time I use a capacitive touch screen or pad, and it actually works.

[oPossum]

Gauge block wringing.

[Ampera]

When I hear a very well recorded, very acoustic song played through good headphones from a good source.

[RoGeorge]

[coppercone2]

i added stability and resolution to the thread title

not sure accuracy is really impressive, i think we notice relative change and stability more then referencing a standard as impressive.

[chris_leyson]

When an optics assembly using a laser diode and photo diode didn't exhibit any precision, stability or resolution but turned itself into a very sensitive microphone. I decided to have a look at what the photo diode was picking up with a cheap web cam and I've never seen so may diffraction rings before or since. It was just luck that it sometimes worked and it was probably as far removed from metrology as you could get.

[Domagoj T]

By pure chance I ended up on a trap shooting range where I was given a shotgun and told to yell "PULL!".
I'm not a gun nut, but the shotgun was a masterpiece. Not only it had some very intricate engravings but the mechanical aspect of it is something I was astounded by. It was a vertical double barrel break action thing that was increadibly smoot. It used almost no effort to close the barrel and produce a very positive and distinct click and likewise would open with just a small smooth lever. It would also eject the spent cartrige(s) with just the right amount of force so it goes over your sholder but doesn't fly like crazy and punch someones eye out.
I was thoroughly impressed by the machining of it.

[RoGeorge]

When an optics assembly using a laser diode and photo diode didn't exhibit any precision, stability or resolution but turned itself into a very sensitive microphone. I decided to have a look at what the photo diode was picking up with a cheap web cam and I've never seen so may diffraction rings before or since. It was just luck that it sometimes worked and it was probably as far removed from metrology as you could get.

Like this?

[m98]

Watching water evaporate from a beaker in real time or being able to weigh single dust particles on an analytical scale is quite impressive.

[nfmax]

While developing an optical pressure sensor, resolving pressure changes that corresponded to a movement of the diaphragm by less than the size of a hydrogen atom (even though the sensor wasn't actually meeting it's resolution specification at the time). Also having to check that the gravitational redshift of the light travelling down the fibre to the bottom of the oil well wasn't a significant source of error (it wasn't)

[coppercone2]

what is an optical pressure sensor supposed to do? measure light intensity by how much force it exerts?

[RoGeorge]

Testing an I2C digital temperature sensor (TMP112, 0.0625*C resolution), and ended up with an unintended breath detector! 
https://hackaday.io/project/2823-how-are-you-errr-are-you-alive



The algorithm used in the video is trivial:  An infinite loop which shine red if previous measured temp was lower (heating), and green if previous measured was higher or equal with the current measured temp (cooling).

The accuracy wasn't spectacular (0.5*C), yet the 62.5mK resolution was good enough to sense the breath, or the heat from a hand placed near the sensor 

[NiHaoMike]

Watching water evaporate from a beaker in real time or being able to weigh single dust particles on an analytical scale is quite impressive.

I remember that very well in college chemistry class - how am I supposed to note the value if it's constantly counting down?

[chris_leyson]

@RoGeorge. I don't think it was the lasers photodiode picking anything up although it might have played a small part. The optical arrangment was a laser diode followed by a slit and a spherical uncoated colimating lens, a short measurement path of a few cm, another spherical uncoated lens to focus the colimated beam onto the detector diode and another slit. The slits were suposed to act as apertures but probably introduced some diffraction and the spherical lenses were held in place by nice shiny brass rings with lovely sharp edges, ooh look more diffraction patterns. You could also adjust the position of the detector diode for "optimum response" whatever that was. I think that in the sensor I had the detector diode was so far off the optical path it was picking up an "outermost" fringe and probably that is why it worked well as a microphone, eventually I moved the sensor a little bit and I couldn't get it to work as a microphone again, I think it was just luck. It was supposed to detect a change in wire diameter and I think they sometimes worked more by luck than by design.

Never thought of using a lasers photo diode as part of a interferometer, but a cool experiment. 

I've seen people setting up 50mW laser diodes for 30mW measured power after a colimating lens, if you angle the power meter just right you can reflect a lot of energy back through the colimating lens and into the laser diode. The end result is that now you've got maybe twice as much photo current being generated by the lasers photodetector. Set the laser control loop up for that amount of photocurrent and it's no wonder that the laser failed maybe hours of days later, because it's set for the wrong photocurrent and it's trying to gererate more power than it's rated absolute maximum. I used to make sure that the reflected beam coming back from the power meter just missed the laser diode and never had any problems.

[cdev]

Use of precise measurement in GPS for measuring very small distances and movements. For example, shifts over large areas due to earthquakes, glacial rebound, or even plate tectonics.

Experiments that measure relativistic effects by differences in timing measured in different environments.

Use of multiple measurement technologies, for example, GPS combined with photogrammetry and 3D reconstruction to generate a picture of what a site likely looked like hundreds or thousands of years ago.

[nfmax]

what is an optical pressure sensor supposed to do? measure light intensity by how much force it exerts?

Measuring fluid pressure in the wellbore. It used an optical interferometer to measure deflection of a flexible diaphragm under applied pressure. Resolution was around 0.005 PSI in a full scale range of 20,000 PSI: accuracy about +/- 1 PSI (apologies for the units - this was the oil & gas industry). Working temperature up to 250 ˚C

[floobydust]

It was my first digital multimeter as a kid, a $99 kit for 3-1/2 digits in 1978. Sabtronics 2000.
Compared to the analog meters I had been using, it was incredible.  MC14433 A/D and unknown TO-92 2.5V reference IC's.

[RoGeorge]

Just because it's Sunday:



 

[tszaboo]

I jumped to deep water with a LTZ1000 design and a 3458A.