Update of two cells from a cell.
 

Hello group such good day.
Do I make myself clear:
A1 I have a cell that can enter values manually, for example numbers: 1, 2, 3, etc.
I have the cell B1 has a value of cell A1.
ie if A1 = 2, B1 B1 = 2 should appear.
Now
if I modify: A1 = 3, cell B1 MUST REMAIN 2 (B1 = 2).
and in cell B2 it says the new value A1 (B2 = 3) should appear.

if not understood, there is a way to do with formulas ?, or if any macros,
if I could give an idea of a macro, because I'm not very familiar with macros theme.

thanks for the reply you can give me a greeting.