Hello, ellipse perimeter formulas are easily found on google, but I can't find any that are extremely accurate and easily usable.
I found several calculators (and formulas) that came to the same or similar figure, but they are not precise enough.
I measured a 53 x 25 ellipse (very close accuracy), calculated the perimeter (approx 130). I intended to space 60 holes on the line, so I spaced my caliper accordingly, went around and ended up with 62 holes.
Given, even misplacing the caliper a 1/16 of an inch will throw it off, maybe even two holes, I'm quite confident the formula simply wasn't accurate enough.