Phil,

A form with three text boxes.
Hide the first and second boxes so as to
force the user to enter the third box first.
Check it's value is = 0 and <=1.
Show the second box and get the user to enter the second value.
Check if this is = 0 and =< (1 - third value)
Show the first box.
It will be 1 - second value - third value.
(could be 1 - 0 - 0, as in your example)
There's no need to get the user to input anything in this box as you can
calculate it.

HTH
Henry


"Phil Hageman" wrote in message
...
I need a "Weighting" sub for a worksheet module:

The sum of values in cells AI19, AI22, AI25 must equal 1.0.

One or two of the cells may be blank - the remaining cell
(s) must equal 1.0.

The worksheet initially opens with all three cells blank -
this is acceptable. However, once an entry is made in the
first cell, the sub takes over, and a message should ask
if the others are to be populated. If "No", then the
populated cell must equal 1.0 (if 1.0 msg to resolve);
if "Yes" wait for an entry in the next cell. After an
entry in the second cell, a message should ask if the last
cell is to be populated. If "No", then the two populated
cells must equal 1.0 (if 1.0 msg msg to resolve);
if "Yes" wait for an entry in the last cell. When the
entry is made in the last cell, the sum of the three cells
must equal 1.0 (if 1.0 msg to resolve).

Thanks,
Phil