In order to save the user from repeated typing of complex command line strings, it is possible to define functions which carry out lists of commands. These user-defined functions consist of strings of basic commands and may include previously defined functions, with up to 5 levels of nesting permitted. (Nesting functions deeper than the five permitted levels will cause an error message to appear on screen 1, and the illegal lower levels will be ignored.) Data-taking routine activations (CAL, PS, MAP, etc.) may be incorporated in functions and can be strung together, since the remainder of a function will not be processed until the current action has been completed.
Twenty-four user-defined functions are allowed; four of these, though, have the fixed names: FNA, FNB, FNC, and FND. The specially named functions FNA, FNB, and FNC can be initiated either through the keyboard or via the pushbuttons on the telescope control panel marked FUNCTION A, FUNCTION B and FUNCTION C (The FND function is not currently implemented in this way and has been defined for possible future expansion). The FUNCTION buttons are only usable when the observer is in the KEYBOARD mode and sensor 11 is turned on.
!!! Use of a function button causes the observer to enter KEYBOARD mode and will flush the command buffer of all currently queued commands. See section 2.4.2.3 below.