http://en.wikipedia.org/wiki/Watt_balance

The long-term goal of these experiments is to produce a new definition of the kilogram based on fundamental SI units, to replace the present definition based on the International Prototype Kilogram
I thought that the kilogram is an arbitrary measurement. Is it not? What are they trying to achieve?

The watt balance is a more accurate version of the ampere balance, in which the force between two current-carrying coils is measured and then used to calculate the magnitude of the current.
I thought our definition of an ampere is also arbitrary....although seeing as the SI units try to be a symmetrical as possible, they should not have chosen 6.24150948×10^18 electrons unless it was necessary.

The ampere was originally defined as one tenth of the CGS system electromagnetic unit of current (now known as the abampere), the amount of current which generates a force of two dynes per centimetre of length between two wires one centimetre apart.
So how did they choose this definition? This is not like Plank's constant where the value is an actual property of nature unalterable by our means. Yes, you could change the definition of jewel seconds to anything else, but the new unit will still be proportionally alterable. As in, if you made the value waka seconds to possess 2x the current energy of Js, the numbers of waka seconds would be 2x less than jewel seconds. The fact remains that what a quanta is cannot be changed, only varied in the power of each unit and their proportioned number.