I am not familiar with Rooy standards, and cannot confirm whether or not, or how, similar they are to Underwood standards, but if you want information on Underwood standard backspace adjustments, I would check out the Ames service manual for standards located at the bottom of the page here.

I was just looking at the service manual for adjusting the backspace on an Underwood. I am not sure how familiar you are with typewriter repair, but if you are new to typewriters, I would advise leaving it alone for now and just push the carriage back a space with your hand if you need to. I had an Underwood model that didn't come with a backspace, and it wasn't a huge deal to just move the carriage manually when I needed to. If you really want to try the repair, the instructions for an Underwood backspace adjustment is on page 122 of the Ames Vol 1 Standard Service manual (page 126 of the pdf scan), which can be found in the link of my previous post.