Here’s an excerpt from a topic about temperature compensators in exponential converters on Modwiggler forum:
Frequency drift is caused by the two transistors in the exponential converter being at different temperatures and minimised by them being on the same substrate. This is temperature balancing. Temperature compensation with tempco resistors tries to stop the Volts/oct changing by matching the exponential term which is proportional to absolute temperature. At 25 deg C the amount of change for 1 deg is 1/(273 + 25) = 0.33557% or 3355.7ppm. That is where the figure comes from, it is not 3300pmm or 3000ppm or 3500ppm or anything else.