Code:
...procedure Taccounts .Checkvalue(Sender: TObject);
var
f : TCalculation ; // i have created an instance of TCalculation
begin
if f.Newvalue = True then // i have called the boolean
End;
... but you are not accessing the instance your have created. Instead, you
access 'f', which is undefined at this point.
Where is your created instance of 'TCalculation'?