Measuring degrees of advance

[Steve51]

I inherited a 51 Custom sedan from my father. Has the 8ba v8. The small white dimple on the crank pulley is at 4 degrees btdc to my understanding. So when one sees recommended degrees of advance at certain rpm are these measured from the mark at btdc or is it measured from tdc? As an example if you want 24 degrees of total advance is it actually 20 from the dimple plus the 4 to tdc making it 24 or 24 from the dimple?