User blog comment:I am a McCree God/Marckerxallum/@comment-32783837-20171223135221/@comment-30754445-20171223193243

He didn't.

The approximation given is completely wrong (I'm not even sure how we should read it, but either way - it is way too small)

At any rate, such numbers are actually quite easy calculate, because:

y [n arrows] x ~ 10 [n arrows x] to incredible precision when x itself is a tetrational number and y as a smallish number (like 650).

So:

650↑↑↑↑650 = (650↑↑↑)648650↑↑↑650 = (650↑↑↑)648(650↑↑)648650↑↑650 ~ (10↑↑↑)648(10↑↑)648650↑↑650

And that last 650↑↑650 can be calculated either by hand or with hypercalc to get:

(10↑↑↑)648(10↑↑)648(10↑)6491828.842838173