Concerning the history of the "invention" of rectilinear Cartesian coordinates, Philip E.B. Jourdain writes, in his book "The Nature of Mathematics", that "Sometimes the axes are not chosen at right angles to one another, but it is nearly always far simpler to do so. . ."
Can anyone point me in the direction of applications in which the axes chosen are not at right angles, or perhaps lack orthogonality or rectilinearity? I am struggling with such an application, in which I have no way around the necessity of at least beginning with such non-standard axis definitions.
I have worked out a good deal of the arithmetic I need to handle my problem, but I sure would like to read what other people have done.
If you reply, please also send it to my email address, lest I miss you: