C1

C

C1 – C

A2

A

A2 – A

B2

B

B2 – B

C2

C

C2 – C

A3

(A1 + A2)/2

A3 – (A1 + A2)/2

B3

(B1 + B2)/2

B3 – (B1 + B2)/2

C3

(C1 + C2)/2

C3 − (C1 + C2)/2