How are G, ħ and c measured?

[Garrulo]

How are G, ħ & c measured??

 

[PAllen]

Did you make any attempt to answer this on your own? As shown by the most trivial look up, you find that c is defined (not measured), and the measures of the others are described as below:

http://en.wikipedia.org/wiki/Speed_of_light
http://en.wikipedia.org/wiki/Gravitational_constant#History_of_measurement
http://en.wikipedia.org/wiki/Planck_constant#Determination

All of them may considered defined in some systems of units (for example, G is simply defined as 1 in some unit systems).

 

[mfb]

Wikipedia and Google are better starting points for basic question like this.