some help with math

[Art]

But wait there’s more!
If you call within the next 20 minutes I’ll also throw in this rotating bit
(but also found I broke it and got to steal some memory back)

thingyousubtract var byte ‘ new variable
thingyousubtract = 0

   if val < 6 AND Menu_Select = 211 then 
   thingyousubtract = 0 : gosub memorysaverotate
   endif 
   if val =>6  and val <= 11 and Menu_Select = 2112 then 
   thingyousubtract = 6 : gosub memorysaverotate 
   endif
   if val =>12 and Menu_Select = 2113 then
   thingyousubtract = 12 : gosub memorysaverotate 
   endif

memorysaverotate:
val = 1<<(val-thingyousubtract)
goto Show_current_sel_2