Circular Reference with Iteration
 

Hi. New to the board, new to Excel, not new to this Earth.

I have created worksheet to accumulate totals.
Cell A1 - to input latest amount
Cell B1 - to display previous accumulated total prior to latest input at A1
formulae used =+C1
Cell C1 - to display new accumulated total
Formulae used =A1+B1
This creates Circular Reference (B1 and C1 trying to read each other) so I have set Iteration at max1.
This works wonderfully well if A1 is the only cell where I enter data, but, when entering data further into the spreadsheet - cells not linked by any formulae to the 3 mentioned - they repeat their accumulation giving false totals.
So the question is:
Can I preset a disable or isolate on this circular reference whilst entering data
elsewhere? or,
Can I add some form of 'Activate' button which will operate the accumulation and not allow non-activate repeats? or,
Anyone know a better way of achieving target?

Apologies for pre-amble, I come from a pre-techno age.
Thanks in hope
Phil