Hi guys, here's a method I am currently using to get precise tap tempo for dotted 8th delays, especially useful when recording with a virtual metronome.
1.) Set your desired tempo on the metronome.
2.) Divide 60 (the number of seconds per minute) by the tempo you are playing to.
3.) Divide its quotient by 4.
4.) Multiply the result by 3.
5.) Move the decimal point 3 places to the right to get the time in milliseconds for your delay unit.
2.) 60/100 = 0.6
3.) 0.6/4 = 0.15
4.) 0.15 * 3 = 0.45
5.) 0.45 -> 450ms
Note: If the result isn't exact, round off the result to the nearest thousandths before moving the decimal point.
Hope this helps for all you tap tempo guys.