Water temp calibration

What type of thermometer do you think is the most accurate for calibrating your depth finder.? I tried my digital meat thermometer side by side with the transducer and was 8° off. Then I took the ducer out of the water and calibtated it to the NWS air temp. It was 3° off. I now want to check how the air temp calibration compares to the water temp calibration just to see how close together they are. I know ... sounds silly but my inquiring mind wants to know.

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I would use a k-type thermocouple and my Fluke DMM with thermocouple adapter. The FLuke is way more accurate than an inexpensive cooking thermometer, and traceable to the NBS if properly calibrated, but only nerds like me would have one, so use the most accurate digital meter you can find/borrow. Alternatively, use an ice-water slurry in a bucket, put the transducer in there, and calibrate to 32F. Don't forget to "soak" the transducer in the water for a good while to let it fully get to the temp of the water, it may be hot from riding to the lake in the sun.

Also, from what I understand, thermometers are most accurate in the range they are designed for ..... In other words, a body temp. thermometer is most accurate in normal body temp. ranges, while a meat thermometer works best on much higher temps.

I learned this from hatching baby chicks, where a precise temperature is critical to a successful hatch.

Either ice water, or a boiling water bath, depending on altitude, may give an accurate reading around 32*, and 212*, but if your water temp. is somewhere in the middle of these temps., accuracy will probably suffer.