[Tea on tuesday]

Things like precessional dating. It's really an amazing theory in just a few easy steps.

#1- Decide that ancient monuments were designed to mimic the layout of the stars---with no historical backing...also don't forget to omit buildings that "don't work".
#2- Recall that constellations move over time.
#3- Trace back the positions of those constellations until they correctly align with the desired ancient monument
#4- Whoops, there's no match! Don't fret though just look for a date where they closely match
#5- Hey, here's a date where they sort of closely resemble part of this arbitrarily selected constellation!
#6- Determine that date must have been when the monument in question was built!
#7-...
#8-profit.

Also he does a lot of "sacred geometry." But really, his mathematical manipulations pale in comparison to the seminal work of Zecharia Sitchin I'm afraid.

edit: My collection of pseudohistory books is impressively large.