Hi Gregory
A factor of 10. That would suggest incorrect position of a decimal point somewhere or clock speed but James beat me to it.
I think there is one other thing worth mentioning. This concerns step accuracy. I don’t know what flavour Arduino is concerned but some time ago I had occasion to do some measurements on an Arduino UNO R3. Results and description here.
Arduino UNO R3 some limitations
This concerns the accuracy of the “digitalWrite” command. In summary the UNO has a built in error of about 4µSec. Apparently this comes about due to some housekeeping by Arduino before executing the command. This is not too bad at higher delays but when you get down to 10µSec this is 40% so it might be a good idea to measure your rotational speed again with a tachometer. This error can be reduced greatly (confirmed by measurement) by replacing the digitalWrite commands with “digitalWritefast” which bypasses the housekeeping. There are some links in that post to the sources of info.
Other Arduino models might be different. I don’t know.
Cheers Bob
