1/ you create one master calendar that range from first date possible last date possible.
2/ add a calendar type field to that calendar and give a new field called "calendar type" the value "order"
3/ concatenate (duplicate) that calendar table, but without that field "calendar type" and add a new value to "calendar type", with the value "sales".
you now have 1 master calendar that works for both dates, just demand the user to always choose one of the two "date types"
Svebeck Consulting AB