Are custom indicators hard to write?

If you learn step by step they can be fairly easy.

Start by opening the User Functions supplied with SpiffyCharts.
and of course start with the simple functions first.

Many times you can modify an existing function to get what you want.
Save your modified function with a new name and test it.

The most complex functions can often be written stepwise
rather than whole-hog.
Put plenty of comments in your function to help organize your thoughts.

You will notice that the language we use is very similar to those used
in other technical analysis programs, so adapting indcators you see in
trades mags can be very straight forward.