Why am I unable to change the clock period in the MAX PLUS II Waveform Editor?

Description

When you select a signal in the Waveform Editor and choose Overwrite Clock (Edit menu), you can usually change the clock period. However, if the Snap to Grid option (Options menu) is turned on, the default clock period becomes two times the current grid size and you will be unable to change the clock period. To change the clock period, turn off the Snap to Grid option.