I'm trying to convert an old GW Basic program into a more user friendly and
more updateable spreadsheet. I was getting on fine but now that I have
created and implemented a function into the spreadsheet it crashes everytime
data is changed.

The conversion was fine until I came to a repeating loop that calculated the
value of one variable needed to generate a particular value in another. I
have managed to create a working function that does the job. It requires
three values to be called in which come from named cells [i.e. =X1CALC(IE,
JC, JD) ]. Now elsewhere in the spreadsheet are some pull down menus that
alter some of the formulae being used. Every time that the data changes that
is called into the function Excel crashes. I presume that its because the
function will be trying to update itself and can't for some reason. I have
tried only calculating the values on a press of F9 but it still has no
effect. Excel still crashes.

I had a quick try at re writing the function as a Sub and assigning the
values from the cells IE, JC and JD to variables within the Sub but I
couldn't get that to work let alone asigning the output to a cell.

Can anyone help?