For a second (or third) point of calibration the black body target works well for digital units -- they're hard to beat if you need to verify hitting a high cook temp for a lethality CCP with a critical limit above boiling. It's hard to say you're confident in the thermometers' ability to measure 150F or 250F accurately if you only verify calibration at 32F.
https://www.thermowo...m/blackbody-ir/
Without financial support for a selectable high temp unit, a basic ambient cup or block style is an affordable alternative. The confidence level at high temps won't be as good, but it's still better than a single point. Boiling water will be better for most probes, but for IR this is safer and easier to execute.
https://www.thermowo...comparator-cup/
Hi GM,
Links maybe only for IR units ? 1000 US $ !! I believe typical IR accuracy is generally (and acceptably) regarded as below officially calibrated thermocouples ?
I think oil baths are the most common Official technique for (non-crazy) temperatures > 100degC ? Although IMEX they are not particularly user-friendly (fume cupboard).
Some Professional Services use "Smart" Black Box methods. Convenient but IRC also not cheap for infrequent usage.
Perhaps surprisingly I believe some cookers/canners still rely on Hg instruments as a Primary reference.
IMO, it's generally preferable to utilise a Quality, Master, externally calibrated, thermocouple and then self-generate sub-Masters as required. Although some operations may demand dedicated calibrated instruments, eg canning.
Dataloggers are another popular solution of course. At a Price.
IR units are certainly convenient for passive sampling applications though.