Unit of Measure Calculations Backward & Forwards_ Excel VBA Programming

Could use some help with Excel calculating Unit of Measure forwards and backwards for inventory purposes. For example;

A1 = Metal1
B1 = Sq. Ft. On-Hand
C1 = Sheets On-Hand
D1 = Packs On-Hand

where C1 = B1/10
where D1 = C1/10

Want to allow user three count and enter possibilities:
If user enters On-Hand data in B1, VBA calculates C1 & D1
If user counts sheets & then enters On-Hand data in C1, VBA calculates B1 & D1
If user counts packs & then enters On-Hand data in D1, VBA calculates B1 & C1

Both demo codes worked just fine for a single line of data. What is the easiest way to apply sheet changee macro code as written if there are multiple rows of data each with different conversion factors? Example:

A2 = Metal2
B2 = Sq. Ft. On-Hand
C2 = Sheets On-Hand
D2 = Packs On-Hand

where C2 = B2/8
where D2 = C2/8

Hi Very Smart guys... The second example didn't seem to work. Any additional thoughts on VBA for:
A1 = Metal1
B1 = Sq. Ft. On-Hand
C1 = Sheets On-Hand
D1 = Packs On-Hand

where C1 = B1/10
where D1 = C1/10

Want to allow user three count and enter possibilities:
If user enters On-Hand data in B1, VBA calculates C1 & D1
If user counts sheets & then enters On-Hand data in C1, VBA calculates B1 & D1
If user counts packs & then enters On-Hand data in D1, VBA calculates B1 & C1

A2 = Metal2
B2 = Sq. Ft. On-Hand
C2 = Sheets On-Hand
D2 = Packs On-Hand

where C2 = B2/8
where D2 = C2/8

A3 thru A99 would all also need to be independent conversion factors

Thank you very much for looking at it and offering help!!!