I'm pretty sure that `convert_xunits` and `convert_yunits` return copies, so all that happens is the local `X`/`Y` are a view on the input `X`/`Y` after the call to `ravel()`, these are then input to convert units and copies returned. So the input is not modified. I checked this using both 1d and 2d `X` and `Y` and the input is not modified.