# Differencing Two Data Files

You will presented with a standard Windows file box dialog twice.

- The 1st dialog is to open the 1st file.
- The 2nd dialog is to open the 2nd file.

Two data sets are then input into the program

- the 1st file data (you might for instance like to compare the difference between the files with the original data).
- the 1st file - 2nd file. It is assumed that both files are the same size (i.e. the x and y dimensions are the same and the same number of data sets are included). If the files have a different number of data sets Viewer does its best to match up corresponding data sets and then only reads in those that match. NOTE: In the drawing menus this latter data set has (-) before it in the menu to remind you it is the previous data set in the menu minus that data set.

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