How to determine the RPM for all in?

!!LOL!! I ran that way for awhile. The old 70RR, Sig Erson, Holley 800dp, used Prestolite tach drive hemi dist, and Accel points. For "awhile" I used a Tiger/ Delta CD box. This was in the '70RR. Had a great big Jones-Motrola tach mounted behind the tach/ clock cutout in the dash. "Nearly" matched the speedo



We are seriously old. Damn.