Hi Gerald,
There’s a couple of ways you can go about doing this. If you want to be able to see the total liters on the Method screen as well as the print report, you will need to add another custom field to the InvoiceLineItems table to store the value in. You can add actions on the InvoiceLineItems grid to calculate and fill in this field automatically. You can then add this field to your print report.
If you just want this field to be displayed on the print report, you can add a calculated field to your print template. You can do this by following the steps below:
1) Locate InvoiceLine.Invoice in the Field List
2) Right click and select Add Calculated Field
3) Right click the newly calculated field and select Edit Calculated Fields…
4) Select your new calculated field and give it a name
5) Select the ellipsis button in the expression field to build your expression to calculate the field value
6) Once you have finished building your calculated field drag it onto your report
I hope this helps.
-Audisho