Why do refractometers lose calibration so often?

[RaymondL]

Perhaps someone here could chime in on this - refractometers whether the expensive kinds or the cheaper ones do need recalibration at some point, and I'm wondering why they can't seem to stick - for example, I haven't dropped mine, and been careful with it, but every couple of weeks or so my readings read either too high or too low, and when checking with a calibration solution it's off.

Looking at the design of such an instrument I would not think that there are any parts that would go out of alignment and need constant calibration.

 

[jjencek]

I do check mine with a calibration solution once every month or two, but it almost never needs calibrating. I have had to calibrate it 3 times in the last 7 years.

 

[RaymondL]

I do check mine with a calibration solution once every month or two, but it almost never needs calibrating. I have had to calibrate it 3 times in the last 7 years.

Interesting - what brand of refractometer do you have?

 

[jjencek]

Interesting - what brand of refractometer do you have?

I don't know - it has no name on it. It has a little round symbol on it with 6 fishes (5 silver and one orange).

 

[Randy Holmes-Farley]

I'm not certain of the answer, but the only explanation I can think of is the portion of the device that moves when calibrating is not held perfectly still over time, and it moves on its own due to handling, expansion and contraction with temp changes, etc.