I don't know why my excel 2003 new worksheet cannot auto calulate
formula (eg. summation), i need to press F9 and it will refresh and
show the new figure. there is "calculate" word at the left hand bottom
of the screen.

Below email was posted before. I have lost the link that direct me to the
add-in manager that can unhide hidden name.
Can anyone advise me again.
TQ

If given MTBF and standard deviation can the reliabilty be predicted at a
defined operational range using Excels Normaldistribution?
say mtbf = 50, sd= 20, then plug in the operating duration.
NORMDIST(operating duration, 50, 20, true).