Daniel, that is exactly what I needed, thank you. The result is just a beginning and needs a lot of refinement but this is a great starter.
Stoyan, I have other projects in mind where having buttons and perhaps a canvas with more than one graph would be very advantageous but the help pages start with adding something to a screen without saying how to create a screen to which things can be added. Clearly I’m missing something very basic but I’m only just learning the syntax as you can see (I only heard of Desmos a couple of weeks ago) so that will be a “learning opportunity” for the future. Any pointers to taking that first step would be appreciated though.