Regarding the arrows!: I used a bit of a wrong notation for the example I gave in GLMakie beginners help: Multiple sliders and an arrow - #3 by fatteneder
E.g. I used xbase, ybase, xhead, yhead.
Just took another look at the docstring (try ?arrow in the REPL) and noticed that arrows wants arguments like arrows!(ax1, x, y, u, v) where x,y refer to the base point of the arrow(s) to draw and u, v are the directions of the arrow(s) as seen from the base points.
Maybe that helps with clearing up the arrows formulae.