Annunciator alarm time stamp
 

I have 10 rows of annunciator messages

col A will be timestamp
col B will be static annunciator message
Col C will be either 1 or 0 and constantly updated for another remote program

The Col C data is constantly being re-written with new data, even though the
bit status may not change

when I use =IF(C3=1,NOW(),"")) command the time is updated each time the
cell is rewritten. I need the time to remain locked until the remote program
changes the 1 to 0 even though the 1 may be rewritten many times.