UpdateDeviceSize

UpdateDeviceSize writes a value: it updates rather than reads. It takes w (an integer) and h (an integer), and returns nothing.

UpdateDeviceSize(w integer, h integer)

UpdateDeviceSize(1, 1)DO  Sync()LOOP

UpdateDeviceSize is called with values of the types its signature asks for. The DO … LOOP is not decoration: a classic BASIC program ends the moment it runs out of lines, and Sync() is what draws the frame.