Antique Precision Resistance Box

Almost certainly over 100 years old, this resistance box has a specified tolerance of 0.1%. Good even by today's standards.
Amazing catalog from A. Gallenkamp & Co. Ltd.
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[@ydonl]

They tell me constantan has a TC of about 8ppm; so with a 5 degree swing, that's 40ppm already; close to the range you saw. The meter will add or subtract it's own deltas, of course. But... it seems all in the ballpark. Magnanin is supposed to have a lower TC; I think in both alloys, the TC can cover a fairly wide range depending on the specifics of the batch. I just measured a manganin Kelvin Varley divider at about 2ppm, which is pretty comforting, but I've heard manganin given as up to perhaps 7ppm or 10ppm, so... as unique as snowflakes, I guess!
I think you're right about the difference in cost. between the two versions of the box; part of it being the wire itself, and part of it (maybe most of it!) might be hand-tuning the coil resistances. Laboriously. Twelve times. :-)

[@bertoid]

I've got a food warmer/cooler box that I'll be trying to use for tempco measurments. One day...

[@Alan-v7s2h]

Hi, I really like the site content, stuff from my era, keep up the good work. Thanks, Alan.

[@bertoid]

Glad you do, thanks!