I think you just have to decide the pattern you would allow and then parse it accordingly
Names Default To Here(1);
dt = Open("$SAMPLE_DATA/Big Class.jmp");
obj = dt << Distribution(Column(:Height));
pattern_check = "\d+:\d+/\d+";
loop_pattern = "70:90/10";
If(IsMissing(Regex(loop_pattern, pattern_check)),
Throw("Incorrect pattern (" || loop_pattern || ")");
);
minval = Num(Word(1, loop_pattern, ":"));
maxval = Num(Word(2, loop_pattern, ":/"));
inc = Num(Word(-1, loop_pattern, "/"));
increments = Index(minval, maxval, inc);
For Each({increment}, increments,
obj << Tolerance Interval(Alpha(0.95), Proportion(increment/100));
wait(0.5); // for demo purposes
);
show(minval, maxval, inc, increments);
-Jarmo