hi;
you can keep say 6 bytes for reading the number.also put a byte for key counter.
on each key press increment this counter
and buffer it.check if key pressed is "enter".if it is then your entry is complete.
after that with help of counter search for
'.'.then you should be able to identify
digits before and after decimal point.this
should indicate proper multipliers
e.g.if there are 2 digits before decimal
highest factor is 10 and so on.
regards
pranav