I just bought a Craftsman and it said accurate + or - 4%.....??
What wuld you do in your above listed senerio? Tighten it to 25 foot pounds instead of 20??
+/-4% at 25ftlbs = 1ftlb (25x0.04=1)
So a setting of 25ft lbs may actually get 24 ft lbs (25-1) to 26 ft lbs (25+1).
Torque specs are almost always given in ranges.
Set the tool for the center of the range (or to the value specified) and it should be fine.
If you worried about tightening too much (cracking plastic or stripping threads) set the tool for the lower end of the range.
If you want to make sure it's extra tight go for the upper end of the range.
I have snapon and craftsman,but one important thing to remember,torque wrenches are only accurate at 75 to 100 %.If you had a 100 ft lb torque wrench and wanted to tighten something to say 20 ft lbs it would not be accurate.
I just bought a 3/8" drive t-wrench that had a certificate with actual readings at various Foot pounds and it was only off like 1-2 lbs.
If you check your manual for torque specs you will see they give you a range...few pounds either way so unless you use it to make a living dropping big coin on a torque wrench is a waste of money imo, the key is to get all the fasteners torqued the same and a cheapo one will do that for you