How do I improve my FPS counter? Mine is ok but it only updates every second therefore only have a 1/60 chance of seeing slow down :/

I show you an example as follows. DIM ITV[60]:FILL ITV,0 PTR=0:PMS=MILLISEC 'START OF LOOP ITV[PTR]=MILLISEC-PMS PMS=MILLISEC:PTR=(PTR+1)MOD 60:TTL=0 FOR I=0 TO 59:TTL=TTL+ITV[I]:NEXT I IF TTL!=0 THEN FPS=60/(TTL/1000) ELSE FPS=0 LOCATE 2,2:?FORMAT$("%6.1F FPS",FPS) 'END OF LOOP