Replacing Precision Resistors, TT-1A

[Winky Dink]

I'm reconditioning this Heathkit tube tester, and other than replacing paper and electrolytic caps; diodes; and a few drifted resistors, everything looks pretty good. I'm replacing two or three of the 1% resistors, and I'd like to know what characteristics qualify a "precision resistor." Is the precision resistor less likely to drift? Why shouldn't I replace a 100 ohm 1% resistor with a 5% resistor that measures exactly 100 ohms?

I ordered all the replacement parts last night, but it took me quite a while to find three 1% resistors in the values (or combinations) that I needed.

I said that everything looks good, but I have one concern with the original 1% resistors. There are ten precision resistors, and they're all spot-on except for two that have drifted 5 to 10 percent lower. Both of the drifters are on the same switch, and a third 1% resistor on the same switch hasn't drifted, but looks like it might have been burned. Is this possibly an indication of a wiring error?

I'm using TT-1A restoration guides available online from Kent Nickerson and RDF Products (thanks, guys), and I have an original assembly manual on order.