timing advance question

The other day i was looking at the timing in my car and setting it. I set it at 10*BTDC as a baseline. Then i revved it to 2500rpm and the timing advanced by 10* more (mechanical advance) for a total of 20*. Then i added the vacuum advance for another 10* increase (total of 30*). I know it was at 2500rpm because i had a 4 gas analyzer hooked up with the tach pickup hooked up. I tried looking for specs for total timing advance, but couldn't find anything in any of my sources about this. Is this correct or is something off? I'm not having any driveability problems, but i'm just curious as to what the spec is. Thanks.

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'84 Mustang 5.0 T5, FMS aluminum radiator & 180* thermostat, 1 5/8 shortys/2.5" duals, '88 GT tail lights and wheels, Holley 4160 4 BBL, smog pump idler, more coming soon