This is the first time film goers are introduced to R2-D2, This unit is the Peteric unit number 3 which is the Remote Control unit with the center foot.

This unit is often referred to as "Old Rivety" due to the visible repairs made in the mechanical arm region.

The dome on this unit appears to have the "Plaster Study" panel spacing. Which is easiest to identify by looking at the placement of the front reading lamp between its neighboring blue panels.