SPSS User Guide (Math 150) [licensed for non-commercial use only] / Transform → Compute Variable
How to calculate the average of a construct | Analysis INN.
SAGE Research Methods Datasets Part 2 - Learn About Rescaling and Transforming Variables in Survey Data in SPSS With Data From the National Survey of Sexual Attitudes and Lifestyles (2010–12)
Compute and IF (introduction)
Using SPSS and PASW/Computing Variables - Wikibooks, open books for an open world