The way I interpret this is thus:
Lateral direction is established by the equipment - let's say the tube bundles are in the Z direction, then lateral is X.
I can either 1) move up to 1/4 inch in positive X and up to 1/4 inch in -X direction, or, 2) move up to 1/2 inch in +X direction and 0 in -X direction , or, 3) move up to 1/2 inch in -X direction and 0 in +X direction.
I could be wrong though.
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Dave Diehl