Which variable, and at which point?
Note that
(~exist('Pressure'))
tests whether Pressure exists as any of a number of kinds of object, then takes the logical negation of the result, and displays it to the screen, without using it in computation.
Some of your files might have variables defined that others do not. You should be clear'ing variables that are potentially loaded from the file, as otherwise the data from the previous file might be still be in memory.
