how often do you calibrate your refractometer?

Not nearly as often as I should...
I've been lucky that it hasn't really ever moved and it always calibrates just as it should. I guess maybe that's why I got in the habit of not really checking it.
I have heard of several incidents where faulty refract readings have led to tank problems.

 

I read that you should always calibrate it before use. I got the Milwaukee digital one and I'll never look back. But that's not feasible for everyone.

If you keep it in the same place all the time, theoretically you should be able to let ti go without recalibration for quite a long time. Always calibrate with 35ppt solution not RODI. Also the refractometer type matters. Most are brine refractometers that measure a wide range, like 0-50ppt. The Pro on one Marine Depot is only for 20-40ppt and according to them is made for true seawater not brine or saltwater. It's much more accurate.

 

Milwaukee says that you're supposed to calibrate it before each use. Probably overkill but I get a vial of room temp RODI ready before I test and calibrate it before I test, then after testing I dab out the test sample with a paper towel, fill with RODI and wipe dry with a glasses cleaning cloth. The sample is so small that any residual saltwater can throw off the next reading (if you're testing multiple samples back to back). I use old syringes from Salifert test kits to add the sample or RODI then use the syringe to suck out the sample before wiping it off. I used to calibrate between each individual test but after using it for a while I determined that that was definitely overkill

I've read that if you have a problem with the meter, Milwaukee will ask you if you follow a procedure like this - keeping it clean and calibrating it often.