Understanding Society User Support

I am currently working with the BHPS data and I would like to add in wave 2 from UKHLS.
I am struggling to make some of the variables comparable between the two surveys.
I am working on earnings dynamics and I use the variable "annual labour income" from BHPS
"fiyrl". Which is the equivalent variable in the UKHLS? I thought that the variable "b_prearna" total earnings annually
could be comparable but I have just figured out that the variable is not continuous.
Can you suggest me any documentations that can help me in solving this issue?

many thanks in advance for your kind reply