Old tv timing math trick

[Dave A]

I have no idea who taught this to me in the early 70's in my early tv directing days. It is a math trick to turn HH/MM/SS in to a calculator math add/subtract entry to get show segment timings. Segments/commercials/station ID, etc. to keep the show on time on the air or taping.

Nor do I know why I remembered this tonight. A neuron just fired in good order and this is as off-topic as I can find. Just for fun here from an old director.

It works like this. If you want to add 5:32 and 6:18 you would enter 5032+6018 (0/zero subs for : on your early calculator) and get 11052 which equals 11:52. And this works in reverse for subtracting times.

Now the problem. If you add 4045 and 7034 you get 11079 which is an overflow past :59. And there is a fix. Just add 940 and you get 12019 or 12:19. Same for subtracting but use -940.

If the overflow was only in the MM/SS you would only use 940 once. If it was across the board you would use 940940 to fix. If it was just the HH/MM overflow you would use 940000. I just did it as it appeared and did not let it get too far down the road.

As I remember, this is sexidecimal math. That is the end of my math knowledge on this but it worked wonders for me for years trying to time long shows I was directing. I kept track of the segments already on tape adding in the commercial time and end time for the station break. When I got to the last segment I already knew exactly how long it should be to keep the show on time for air. If it was the live afternoon 16mm movie and I knew I did not have enough time for the last segment I would just roll-off some of the movie to make up the time. The butler still did it. I wore out a few RCA 3C3030 calculators on this...and still have one today at work for billing.

[jr_tech]

Nice shortcut! I guess we can blame the need for this calculation on the Babylons.

https://en.m.wikipedia.org/wiki/Sexagesimal

Interesting history!

jr

[Dave A]

Sexagesimal...a new word to me. Sexidecimal does sound 10 based. A great read jr. Now I have to find the genius Babylon/NBC descendant that figured the 940 conversion. Wait...maybe that is what Michael Rennie was doing on the chalkboard to Sam Jaffe's calculations in The Day the Earth Stood Still. I have to be careful. I could stop the earth with a simple 940 miscalculation and the Babylonian empire could return.

[old_tv_nut]

Replacing the colon with zero puts the larger unit in decimal thousands place.
Adding 940 is the same as simultaneously adding 1000, bumping up the larger unit by 1, and subtracting 60, leaving the correct residue for the smaller unit. Much easier to do on a simple decimal calculator as a single addition to a single number, compared to keeping track of minutes and seconds separately, which the calculator won't do.