Hello all, I have never understood the tables. Mptune/calculated tables/full throttle total timing/rpm vs psi chart. In the upper right hand corner is a blacked out box with teal letters that says...X:27.817 (in/Hg) Y: 19.325 (degrees). What do these numbers represent beyond the obvious nomenclature? Are these numbers related in some way to the PSI vs RPM charts.
Additionally If I pick out any X-Y juncture, what does the number displayed in the box represent, timing, corrections to timing or some other function.

Is there a resource that explains these things?

If you can help, thanks!