if i use a simple code
Code:
//press F11 to run
#include <acknex.h>
#include <default.c>

var def_dfps;
var def_dfps_lo;
var def_dfps_hi;
	var var_dfps_lo, var_dfps_hi;


PANEL* pnl_fps = {
//	digits(10, 150, "time_frame %5.2f", *, 16, time_frame);
//	digits(10, 160, "fps        %5.0f", *, 16, def_dfps);
	digits(10, 170, "fps lo     %5.0f", *, 16, def_dfps_lo);
	digits(10, 180, "fps hi     %5.0f", *, 16, def_dfps_hi);
	flags = SHOW;
}

void hi_lo(){
	
	int i;
	while(1){
		var_dfps_lo = minv(var_dfps_lo, def_dfps);
		var_dfps_hi = maxv(var_dfps_hi, def_dfps);
		wait(1);
	}
}

void main(){
	hi_lo();
	while(1){
		def_dfps_lo = var_dfps_lo;
		def_dfps_hi = var_dfps_hi;
		var_dfps_lo = 1000;
		var_dfps_hi = 0;
		wait(-1);
	}
}

for determining peak and lo of fps rate per second

i get from 350 - 500, though no additional programs are running, but not necessarily at regular intervals

sys: Intel CPU 2140 @ 1.60Ghz, 4GB RAM, Window Vista SP1, NVIDIA GeForce 7300LE

Hope this helps