Hello LarryC,

The act of changing any cell on the worksheet triggers the WorkSheet_Change() event. When you change a cell within the event procedure, the procedure is called again, and again,and again until the stack overflows and Excel becomes unstable or crashes. This known as a "Cascade Event Failure". The addition of the 2 line of code prevent the event from retriggering while the event procedure modifies cells, and switches it back on for normal operation when done.

Sincerely,
Leith Ross