Purpose of column LB in CPTs

I notice that the last column of the CPT files have a L or B. What do they mean? What are they for?

The optional flag A is used to indicate annotation of the color scale when plotted using colorbar. The optional flag A may be L , U , or B to select annotation of the lower, upper, or both limits of the particular z -slice, respectively.

See General Features — GMT 6.1.1 documentation (generic-mapping-tools.org)

Thanks.I couldn’t find it.

So, If I want to combine 2 CPT with the following commands, could this produce an error?

gmt makecpt -Cabyss -T$MIN/0  -N >  $color
gmt makecpt -Cdem2  -T0/$MAX     >> $color

Because I noticed that the last columns always have an L except for the last record (where there is a B). However, with the previous commands I get a B and the end of each sub-set.

It should work. You can try to plot the CPT file to check it.

Given two separate and unconnected makecpt calls there is no way for these to know things are being stitched together and hence the middle B should be L. So I think this is a rare enough case that a manual edit is reasonable.