Thanks - strange as I thought I had done that already. But it still leads me on to the actual problem I have.
The Fieldname from the list is called Cost, the card item text input box is called CrdCostData and this text box initially had TextFormat.Number in the format property. I have tried each of the following in the Format property box:
Text(ThisItem, "####.##")
Text(ThisItem.Cost, "####.##")
Text(ThisItem.CrdCostData, "####.##")
Text(TextFormat.Number, "####.##")
but it doesn't format the number at all. What should I put here?