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'.
In 17-32, the corners traditionally set one bar to the person you just passed, then one bar to the next person to pass. In a variant for [19-24] 1c turns BH in PdB.
The first two turns are in Strathspey time, the second two are in Reel time.
The original tune is a hornpipe
Note: Cosh explicitly tells 1c to pass Lsh in [9-24]; however the Rsh pass is quite common, and nicknamed »Mairi's Divorce«.