[BillA]

there is a guy selling these things pretty regularly over the last several years on eBay (search Schmermund)
for different temps different matls are used
the thermometer is only $350, but the cells . . . whew

it still gets back to the PRTD's non-linearity over our range of interest
no way to avoid creating a cal curve that I know of, at 1/3 DIN they are pretty much the same - but still have a curve

of course, on the censored forum the resident wizard has concluded that 0.1°C resolution is sufficient for WCing component testing, we do love to pick the pepper