I came across a spec (tolerance level) of each type of resistors that could be used to do the mod.
1. Cermet multi-turn: +/- 10%
2. Carbon film (fixed): +/- 5% or +/- 10% (gold or silver band)
3. Carbon pot: +/- 20%
4. Metal film (fixed): +/- 1%
Based on the above info, it could be said that a metal film resistor offers the lowest tolerance level and should be used to do the mod to min the flucuation/variation in volt.
Source: http://www.velleman.be/
