3rd Kyū

The endpoint of an anti-diagonal is always a square on the h-file or the 1st rank.

Consider tracing down-right (↘). The steps to the h-file is "8 - file value", and the steps to the 1st rank is "rank value - 1".

For a bishop on c3, steps to the h-file: 8 - 3 = 5, steps to the 1st rank: 3 - 1 = 2.

The 1st rank is reached first, so adding 2 to the file gives 3 + 2 = 5, and the endpoint is e1.

For a bishop on f7, steps to the h-file: 8 - 6 = 2, steps to the 1st rank: 7 - 1 = 6.

The h-file is reached first, so subtracting 2 from the rank gives 7 - 2 = 5, and the endpoint is h5.

When both step counts are equal, the endpoint is always h1.