PERMNO   date         monthyear  PRC       RET
10001    1990-01-02   199001     10.1250   0.0000
10001    1990-01-03   199001     10.0000  -0.0123
10001    1990-02-01   199002     10.0000   0.0000
10001    1990-02-02   199002     10.0625   0.0062
...
10002    1990-01-02   199001      6.1250   0.0000
10002    1990-01-03   199001      6.1250   0.0000
10002    1990-02-01   199002      6.2500   0.0204
10002    1990-02-02   199002      6.2500   0.0000
...

PERMNO   date         monthyear  PRC       RET      MonthlyReturn
10001    1990-01-02   199001     10.1250   0.0000   0.1000
10001    1990-01-03   199001     10.0000  -0.0123   0.1000
10001    1990-02-01   199002     10.0000   0.0000   0.0987
10001    1990-02-02   199002     10.0625   0.0062   0.0987
...
10002    1990-01-02   199001      6.1250   0.0000  -0.0034
10002    1990-01-03   199001      6.1250   0.0127  -0.0034
10002    1990-02-01   199002      6.2500   0.0000   0.2340
10002    1990-02-02   199002      6.2500   0.0059   0.2340
...