[aerohead]

Originally Posted by AeroMcAeroFace

I have no doubt that the measured value in the wind tunnel was to 4 or even 5 decimal places. However, the published number was to two decimal places.

Agreed, on the tiny change from a radiator shutter, they will do measurements down to 3,4 or 5 decimal places. However, that doesn't necessarily reflect in the published data, if the cD was actually 0.304 and then a radiator shutter was added that reduced the drag to an actual 0.299, the published number is still going to be 0.30.

The difference may be 1.6%, but it would be erroneous to claim that because the initial figure was 0.30 and there is a 1.6% reduction, that the new drag coefficient is 0.295.

Because as we see in the above example the actual figure is 0.299.



You are confusing accuracy of measurements with precision, read about it here https://en.wikipedia.org/wiki/Accuracy_and_precision.

please see my # 28 permalink below