Thomsen,

Actually, the limit has to do with the amount of script that can be entered
into
the "definition" text box when defining a function. The limit is roughly 250
characters. However, in terms of the ACTUAL length of the fitting function,
there is theoretically no limit. The reason why is this:

Suppose you define a fitting function as follows:

y = a + x * b;

Logically you would enter this directly into the "definition" text box since
it is so simple. However, this same function can be used in a fitting process
by creating a text file (filename.txt) that contains the function in a section
called [MyFunc]. This method would require that you enter a run.section in
"definition" text box of the fitter that will call [MyFunc] instead of
actually
defining the function in there. The "definition" text box would therefore have

the following appearance:

run.section(filename.txt, MyFunc);

Be sure to set the Form drop down list to Y-script to ensure that this works.

Along with this you would need to create the text file that contains the
fitting
function in a section such as the following:

[MyFunc]
y = a + x * b;

Save this text file (filename.txt) to your Origin directory so that Origin can

find it during the fitting session.

If this does not make sense please respond to my posting and I can try to
explain further.