How to add totals in a form/report.

Hi I need a total value to show the total value of a harvets event/month/year

With this link I show a page for a garden site. In  this site also cost and harvest are logged. Th page shows an example for a harvest event.
www.fluve.nl/index.php/tuin-logboek/tuin...-week-september-2023 .

The harvest is in bottom tab "Oogst"
I need to add the sum of values in Column "Waarde".  Field "Waarde" is part of repeating fieldgroup "Oogstdetail", within Type: "Tuinoogst".
I tried to figure this out, but can't find a startingpoint.

I have a workaround with sqlquery. The results need much rework in a spreadheet, That is only workable for a year overview.:
Suggestions I appreciate
Regards Henk KV 

i think the best way is to code it in php directly in a layout for your field

Thanks ,
I gues copy a field plugin and create a new field. 
It seems quite a challenge But give it a try.
Regards Henk KV

no in your field you can create a layout
Ex : www.flexicontent.org/documentation/tutor...-for-file-field.html

Micker Thanks,
You put me in the right direction.
However I had t deal with fieldtype text.
This solution only works with non-formatted numeric values.
In Value_defaul.,php I added a variable $tot
and added code:
    // Add prefix / suffix    
    if (!is_numeric($value))
    {
        $field->{$prop}[$n]    = $pretext .  $value . $posttext;
    }

//         add value to total    
    if (is_numeric($value))

    {
        $tot += $value ;
        if($n < array_key_last($values))
        {    
            $field->{$prop}[$n]    = $pretext .  $value . $posttext;
        }
        else
        {
            $field->{$prop}[$n]    = $pretext .  $value . $posttext . "<br /> ===== <br /> ". $pretext .  $tot . $posttext ;    
        }
    }

The result however is that all numeric fields display the sum.
So I made a copy of the textfieldtype as  Euro fieldtype.
After that I removed the changes in the text field type
This is the result
www.fluve.nl/index.php/tuin-logboek/tuin...oogst/2312-oogsten-3
Regards HenkKV

great