Slightly off topic but related. Does anyone have any recommendations for places to buy calibration trays? Can't see the need for anything expensive. I only need 5 equal size trays but they need to be reasonably robust and of a decent size (approx 2ft square). Must be cheap as chips from the right hardware store if I can find which one/what to google. If I need anything more precise I will pay SCS but these should be adequate for a rough check. TIA