

WHen trying to choose a resistor with a tolerance better than 1%, you 
need a trimmer or to screen devices, it can't be made from adding 2 
resitors of 1% value in parallel, since the smaller device will have the 
error of 1% to cope with. 
You have 3 choices;
a) live with the error of 1% tolerance devices for low Q circuits or low 
sensitivity designs
b) buy resistors with better than 1% tolerance (Vishay/Dale)
c) use trimmers or SOT's (Select-On-Test)