Originally Posted by JD-EE
You can, however, find nice stable resistors that hold 0.1% or less over temperature. You can also find nice "NPO" ceramic capacitors that hold within a few dozen ppm/degree C. That's where the temperature variation would come from. Manufacturing tolerances of the capacitors would have to be in the 2.5% range or else trimmed with a parallel resistor for the R in the RC that is calculated and soldered in during manufacture. For reasons of cheap getting it within 1kHz or about 2.5% is "good enough."
My thoughts exactly; nicely put. I might add that it's likely the design of these pingers hasn't changed much in decades (maybe replacing mica caps with NPO ceramic?). Once a design is certified, they probably follow the principle: "if it's not broken, don't fix it."