Do you know all VFP system variables? No? You can donwload sysvar package, unpack and run sysvar.prg.
DO sysvar WITH "c:\list.txt"
After end program, look at file c:\list.txt.
If you want know which variables are read only or which variables command CLEAR ALL reset to default value run sysvarx.prg
DO sysvarx WIHT "c:\listx.txt"
And look to file c:\listx.txt.