How do I create my own function?

Is it possible to create custom functions? I have many things I like to use in all my systems, and if they were functions I could just call them.

You could create indicators that would only represent a "function" and then use the formula call function to refer to it. For example, you can create an indicator called "test" that does a lot of calculations and then reuse it in all of your custom indicators like this: fml("test"), rather than retyping all the code again. This will however not pass any input you might have programmed in your original indicator and will use the default values.

Note: using the Fml() function does slow down the calculation of an indicator.