2 chords. On 2nd chord 1W crosses down to R of P, 2W moves 1 place up and 2M crosses to her place, so 1c faces 2c across.
Notes: The RSCDS prescribes a 4c set, but the tradition is a longwise set 'for as many as will'.
3C Chain Progression was earlier known as Chaperoned Chain Progression
When setting in the centre, the turn is on the second PdB
Repeat once with new centres and cnrs
In some areas the inner dancers who pass to corners stay facing out, and swivel to face inwards during the setting.
Note: Cosh explicitly tells 1c to pass Lsh in [9-24]; however the Rsh pass is quite common, and nicknamed »Mairi's Divorce«.