This morning, I bought six very similar resistors (0.1, 1, 10, 100, 1k, 10k) made by Cambridge Instruments (UK) at an amateur radio rally for £85 the lot. I've just tested them (fortuitously, the lab was at 20C) and they agreed sufficiently closely with my 34470A 7 digit DMM that I probably believe the enormous resistors' calibration values (1987!) rather than the meter - which must have much smaller resistors. I told my wife that these resistors normally live in a temperature-controlled oil bath, "I hope you're not going to do that here." I think that means an oil bath has been vetoed for the moment.