Speed of Light the State of the Problem

In the 15 years since Froome achieved the generally accepted value for the velocity of light as 299 792.5 km/s with an accuracy of about ±1 ×10-6, work has continued in many laboratories to improve this accuracy and to refine the value accepted for c. A summary is given of the major steps which have led to today's recommended value of c = 299 792 458 m/s, with an uncertainty of ±4 × 10-9, and questions are raised concerning the implications of these measurements.