software

Hi,

I was wondering whether anyone can help me with this problem?
Scenario:
Cell A1 is a being used as a 'trigger' I would like to calculate the
length of time the cell has a value of '1'
When A1 changes to 1 I've tried using the =Now() function to get the
current time and then using the =MOD function to extract the time. and
finally using the =Hour x 60 and =Minutes to get a total minute. When
A1 goes to 0 the same thing happens and the two minute totals are
subtracted to get a number of minutes cell A1 had a value of 1. Thats
the theory anyhow, in practice I can't get it to work.
Would this way be the best way of calculating what I'm trying to
achieve?

Any help or ideas would be appreciated

Rich