Primary Chain Adjustment

[1972XlchBobber]

The service manual indicate that between 5/8 and 7/8" slack should be in the primary chain.   This is while adjusting through the oil fill hole.  As I look at the chain with my side cover off I'm not sure how this measurement should be taken.  When I move the chain up and down, is this the distance:

Option A: Compare top of chain with chain lifted up to bottom of chain when chain is pushed down.

Option B: Measure center of chain lifted up to center of chain when chain is pushed down.

Thanks, Mike

[Lew]

Option B