This is an small example of how my actual SPSS data file looks like:

Group Meas1 Meas2
1,00 20,00 50,00
1,00 20,00 50,00
1,00 20,00 50,00
2,00 40,00 45,00
2,00 40,00 45,00
2,00 40,00 45,00
3,00 10,00 40,00
3,00 10,00 40,00
3,00 10,00 40,00
4,00 20,00 35,00
4,00 20,00 35,00
4,00 20,00 35,00

I would like to calculate the difference between 'Meas1' from 'Group' 1 and 'Meas2' from 'Group' 2, the difference between 'Meas1' from 'Group' 2 and 'Meas2' from 'Group' 3 and the difference between 'Meas1' from 'Group' 3 and 'Meas2' from 'Group' 4. The answers of these calculations would be 45-20 = 25, 40-40 = 0 and 35-10 = 25. But how do I perform these calculations in SPSS? Or what is the syntax for this type of calculation? Does anyone know? Many thanks in advance!