Any tips for shifting by time instead of rpm?

[Cisco Kid]

i shift on rpm and the stop comes on with time...i am gonna test a few other options,but i seem to have to formula worked out for what configuration i am running now...my stop comes on at 1.20 in the run and stays on till 2.50-2.90...and then as soon as it comes off the stop i am shifting at 6500...and i have a 434bbc...this weekend i am going to run super pro and i installed the air shifter and going to try to shift on time..but i did realize that the way i am doing it you have to be extra carefull with your throttle stop settings cause the computer predicts 1 thing and its not usually right on,i have learned that from time to time it picks up 1 hundredth in the 1/8 mile and sometimes it picks up almost 2 hundredths in the back end for a total of 3 hundredths on a run...you just gotta find out what works and try to copy the same data and infromation on everyrun...do things the same way each and everythime and more than likely you will find the consistancy you are looking for...flat out runs in the 1/8 mile my car is usually pretty consistant ...you can also adjust where you shift point to help with consistancy...its just all trial and error!!!
good luck