ouput frequency as 2khz to 10khz
Had you used pre and /pre the above would would have been readable (also what are the g_... thingies?)

Anyhow, at 2kHz a pulse will be 0.5ms wide and 10ms which it sems your window is will give an average count of 20. This, however will NOT be stable a frequency.

Basically max variance (in percent) is ((input pulse width) * 100)/(measurement time) ALWAYS rounded up

Erik