When the Royal Oak was initially designed as a time-only piece for the replica Audemars Piguet, other complications were added in this special case shape in a fast speed. You could find the perpetual calendar and moonphase among this present model. BA here is one of the many two-letter materials codes used by AP, and it shows an 18k yellow gold case. The C serial number on the caseback permits us to date it to the late 1980s, as does the elongated “Swiss made” mention and uniform Audemars Piguet signature at the bottom of the dial.
The key point is that the diameter of this replica watch is 39mm, the same dimensions as the original one and thanks to the base caliber 2120 it packs the perpetual complication into a very slim profile. The seller mentions a recent – and light – retouch of the bezel but no impact to the case, which still shows the original chamfers. One more thing to check with any vintage Royal Oak is the bracelet; here it is tight and the clasp does not bear any deep scratches. . 
The Multi-Centerchrono naming says it all: the chronograph complication can be read easily because of the two central hands, a characteristic of the in-house caliber 1300. This Mido also came with a waterproof case made by Borgel (later Taubert Frères), also known as the fake Patek Philippe’s supplier for the coveted chronograph model. Those two pieces notably share features round sunburst pushers, also found on waterproof chronographs from Movado.
The original dial of the replica AP watch shows a pleasing patina, with readable scales and painted numerals. The hands are made as the original; the chronograph hands are often replaced on these models, especially the red one that indicates the elapsed minutes. The movement has been recently serviced, and is indicated as working flawlessly.