Some 16Fs have an 8 level stack, others have a 16 level stack, I believe all 18Fs have at least a 31 level stack. Oshonsoft Basic is a High Level Language and as such a programmer using should expect internal calls when using built in Functions of the language, which do chew up stack space. For example the LCD calls use up to 5 levels of stack, not much much leftover for other nested calls when using a uP that only has an 8 level stack. Proper programming can alleviate too many nested calls to prevent blowouts(stack overflows), but sometimes there is no way around it in BASIC and one must use a uP with a deeper stack. This is no fault of Oshonsoft, he attempts to make BASIC easier to use by providing Functions that allow the programmer more rapid development. In Oshonsoft, one can easily observe current stack usage in the SFRs, to prevent overflows, when stepping through the program.