There are so many company advertized they are manufacturers of ultra high precision resistors both in China and in the world. Most of them even don't understand what is the real ultra precision resistors, the only they care about is the tolarance, they think ultra precision resistors are those with tighten tolerance. 

but there are only few companies in China who can really make ultra-precision resistors.

Amoung them, Thunder Precision Resistor Co., Ltd. is one with more than 20 years experienced professional manufacturer.. 

Thunder Precision Resistor Co., Ltd. has been spent more than 20% of annual profit amount to improve equipment, set up a reliability test laboratory that can make a lot of reliability test of the resistors to increase the performance of the resistors made by Thunder Precision Resistor Co., Ltd..  The laboratory can do failure analysis for most circumstance and situation.