You should call it d/dx bar. Anyway, I love the choice of theta because a while ago I came up with a nice notation for sin and cos and this fits it really well

You should call it d/dx bar. Anyway, I love the choice of theta because a while ago I came up with a nice notation for sin and cos and this fits it really well. When I first learned trig, it was by way of skipping into physics early. I only understood cos as the magic button for getting x components from angles, and y as the button for y components. So my notation is based on this very literal brute understanding. All the symbols are circles with lines on the appropriate sides. sin = -O- (should be overbar) cos = O| -sin = _O_ -cos = |O Why did I make symbols for the negative versions of the same functions? Is minus sign too good for me? No. I did it because you can differentiate by just rotating the symbols clockwise and integrate by rotating counter clockwise. d/dx O| = _O_. The way you defined theta, and the graphical depiction of theta, fits nicely.