Hi, I just happened to measure the 'Blinking' frequencies (on digital pin13) by changing the program delays from 10000 microseconds to 1000 microseconds then to 100 microseconds . In the first instance the frequency I got was 50 Hz (correct value) then in the second instance I got it as 500Hz (also correct value) in the third instance (100uS) it was showing only 4790Hz ( instead of 5000Hz) and when I set the delays to 10uS it was showing 36200Hz instead of 50000Hz. I confirmed the frequency read outs accuracy using a second frequency counter also. Can anybody explain the difference ?!!. Thanks in advance .