Hmmm.....I've now made it work !!
Expr1: Trim(Mid([WC1],InStr(1,[WC1],"_")+1,IIf(InStr(InStr(1,[WC1],"_")+1,[WC1],"_")=0,0,InStr(InStr(1,[WC1],"_")+1,[WC1],"_")-InStr(1,[WC1],"_")-1)))
By adding the -1 at the end of the expression, it...