That's not going to help you. A one second window is not good for a speedo. Too many changes happen in 1 second and your display will be way out date from what's really happening.

It reminds me of the official 'post-mortem' of the Chernobyl accident I once came across at the back of a dusty Library shelf... where the main monitoring computer for the reactor took some 11 minutes to read all the sensors, calculate and display the result for the operators... which means the reactor status as currently displayed was that from 11 minutes earlier...

What they should have done is what I'm recommending for you - Reduce your count to 1/4 or 1/10th of a second and compensate your math accordingly. You'll get a much better feel for what's happening 'real-time' and the increased error is relatively insignificant.

Melanie