I have a Table with one "normal" field and one calculated field.
The calculated field is supposed to be the diffence between the current
records value
and the prior records values.

Currently I have tried the code below but that puts causes an infinite loop
(when Prior is called the current record is commited, which causes another
call to the calculate function which then calls next and causes another
calculate function call, etc, etc, etc...).

  dValue := 0;
  if not DataSet.Bof then
  begin
    dValue := DataSet['V1'];
    DataSet.Prior;
    dPrior := DataSet['V1'];
    DataSet.Next;
    dValue := dValue - dPrior;
  end;
  DataSet['MovingRange'] := dValue;

So is there any way to do this without crashing my machine?

A simple way would be to use a second Table to read the prior record.
--
Finn Tolderlund

"Chris Brandsma" <cwbrand...@hotmail.com> skrev i en meddelelse
news:3cdaad96_2@dnews...

You'll have to use Finn's suggestion of a second table - you can't move
between records during the OnCalcFields event handler because moving will
cause OnCalcFields to be fired again (as you've found out!)

-Dell

You could declare a private variable to hold the previous value in your form,
initialize it to 0 in the FormCreate event, and then use it in your
OnCalcFields event; something like...

MyForm = class(TForm)
private
  FPrevValue: integer;
    .
    .
    .
end;

procedure MyForm.FormCreate(Sender: TObject);
begin
  FPrevValue := 0;
end;

procedure MyForm.MyTableCalcFields(DataSet: TDataSet);
begin
  DataSet['MovingRange'] := DataSet['V1'] - FPrevValue;
  FPrevValue := DataSet['V1'];
end;

hth,
Michael