Required Separation, Table 508.4

[VLADIMIR LEVIN]

This may be a stupid question...
What do the dashes in table 508.4 means?
For example if you look at B to R is a dash, but R to B is a value (1 or 2)

 

[steveray]

Means you are using the table in the wrong direction....

 

[redeyedfly]

There are no stupid questions but this is pushing the boundaries.