Thank you for your question about transcribing using only UEB for technical material.
Your proposed transcription is correct.
Attached is an image file that contains the print you describe as well as the correct simbraille. This includes a grade 1 word indicator at the beginning of the symbols sequence, the letters AB enclosed in braille grouping indicators (in order to make it clear that the arrow is directly above both letters), the two-cell directly over indicator, and the four cells that represent the horizontal bidirectional arrow (as shown on page 63 of the UEB Guidelines for Technical Material).
Again, thank you for the question!