I’m guessing this is pythagoras
So
1->6 that’s a move of 5 (if that makes sense) so let’s square 5 and let’s say that’s A squared
8->1 that’s a move of 7
So let’s square 7 and call that b squared
A squared add b squared = c squared
25+49= 74
Square root of 74; 8.6
I hope this helped, but sorry if it didn’t as it’s based off of an assumption
