### 9.1.1 Notation of unit objects

A unit object has two parts : a real number and a unit expression (a single
unit or a multiplicative combination of units). The two parts are linked by the
character _ ("underscore"). For example 2_m for 2 meters.
For composite units, parenthesis must be used, e.g. 1_(m*s).

If a prefix is put before the unit then the unit is multiplied by a power of
10. For example k or K for kilo (indicate a multiplication by
10^{3}), D for deca (indicate a multiplication by 10), d for
deci (indicate a multiplication by 10^{−1}) etc...

Input :

10.5_m

Output :

a unit object of value 10.5 meters

Input :

10.5_km

Output :

a unit object of value 10.5 kilometers