On 8 Sep, 17:00, "Andrew Mawson"
wrote:

..he..he - showing my age, but in the era of solid carbon resistors it
was very simple. Choose a value slightly lower than you want, then
with the Avo across it on Ohms file a nick in the carbon until it was
spot on.

Works for film resistors too, you just need a triangular needle file
and work along the spiral groove (one slip and it's open circuit
though!).