Measuring TT Speed

I replied to the OP already but I thought I'd add a comment about the calculations for platter speed from the KAB USA website. Please correct me if I have this wrong, but the platter speed calculation didn't mention that when the platter is running slow you have to account for it by either using a negative error, i.e., [1 + (-count/360)] x RPM, or, subtracting the error, i.e., [1 - (count/3600)] x RPM.
Tom

Doh! That should be [1 + (-count/3600)] x RPM.

Lewm, I used a strobe for decades and whatever error is involved is is meaningless sonically. Watching your telephone spin has a hypnotic effect particularly after a few gummies.

Well guys thanks for all the replies with some help from above and you guys I have it sorted out now, thanks....

@edwyun 
The RPM app does have a calibration feature that is very easy to do , but you have to get the premium or paying version.  You also get the option of entering your tables in the database and compare it with others from around the globe. Is around 15 dlls ( i paid in pesos so i can,t remember for sure) but is well worth it.