Ok I tried
I set the tempo to
120BPM and enter "
-50" at "Relative Tempo Change".
I obtein a Tempo at
60BPM witch is the hal of
120BPM! Success!
I decide to cahnge the main Tempo at "160BPM" just to try. I should obtein "80BPM"
But in reality I obtein a "40BPM" Tempo. Fail.
I precise that I'm using Band-in-a-Box for Macintosh Version 2021 (514)