It is my understanding that when determining the official figure,the General Conference on Weights and Measurements took an average of some of the most accurate measurements that were available at the time. But I think that there were variations in each case. So we could assume that either our tools were just not precise enough, or that the speed of light is not actually constant. (or both?) 
I&#x27;m curious, are physicists these days routinely measuring the speed of light, and if so are these measurements consistent?