Located under Admin/Inventory you will find Rate Types.
You may set up as many Rate Types as you like simply by using Add Record.
Any Rate Type can be given a name and a multiplier to meet your purchasing requirements or naming convention.
Rate Types allow Cost calculations by applying a multiplication factor, based on the type of measurement.
The multiplication factor for a Linear Meter (LM) will have one field whereby you multiply by the length. For Square Meter (M2) the multiplication factor will have two fields in which you will multiply Length x Width.