HP 50g Graphing Calculator - Manual (Page 764)

Page 24-4
The functions contained within the FLAG menu are the following:
The operation of these functions is as follows:
SF Set a flag
CF Clear a flag
FS? Returns 1 if flag is set, 0 if not set
FC? Returns 1 if flag is clear (not set), 0 if flag is set
FS?C Tests flag as FS does, then clears it
FC?C Tests flag as FC does, then clears it
STOF Stores new system flag settings
RCLF Recalls existing flag settings
RESET Resets current field values (could be used to reset a flag)
User flags
For programming purposes, flags 1 through 256 are available to the user. They
have no meaning to the calculator operation.