Now you have to specify three points on the bitmap whose 'real life' coordinates are known. Of course, in most cases, you can make use of the axis labels to choose suitable points. Since these three points (labeled as P1, P2 and P3 on the left side of the windows) are used to calculate a conversion matrix from bitmap to 'real life' values there are two rules for their choice:

•Do not choose all three points on one line

•Use large separations between the three points

On the example bitmap which looks like this

I would suggest the following points:

 P1: 0 eV, 40% reflectance

 P2: 0 eV, 0% reflectance

 P3: 30 eV, 0% reflectance

Here are the actions to do:

•Enter in the 'real' section of P1 the values 0 and 0.4 (i.e. 40% reflectance)

•Press the Select button and click on the point on the bitmap with these coordinates

•Check if the program has entered the correct bitmap coordinates in the bitmap section of P1 (I have got 129 and 152 as bitmap coordinates).

Do the same with P2 and P3:

•For P2 set the real values to (0,0) and obtain about (137,673) as bitmap coordinates

•For P3 set the real values to (30,0) and obtain about (920,668) as bitmap coordinates