I am creating a blockflow diagram template for chemical processes.

Within the spreadsheet, various chemicals are listed down the sheet in
various cells of a column(s) with their quantity in the adjacent cell

I make the sheet scaleable by multiplying the quantity for each material by
a scale factor in the cell B3 which I can change. Hence, as I enter each
material quantity I type in the quantity multilied by $B$3. I find this a
very awkward and clunky way of entering the formula, and know this would be
complicated for eventual users to work with.

Ideally, I would like to enter the numbers into the descending column(s) and
the formula (number *$b$3) automatically substituted for the entered number.

Even better would be that as I click on each quantity cell, a dialogue opens
in which to enter the number and the ok button does formula substitution.

Can anyone help?

Thanks, Roger