After CISTRS, on 618 @ West Malling in the late 70s IIRC, the Sedburgh and Kirby Cadet were using:
C - Controls - Full & Free
B - Ballast - Not Fitted
S - Straps
I - Instruments (both of them, or was it 3)
T - Trim
C - Canopy - Not Fitted
B - Brakes - Not Fitted but we do have spoilers - Fully Open and in line, Fully Closed.
Halcyon Days