This country, and the marine industry in particular, is in the throes of a change that it has been decided shall be called metrication. It is evident from what is both written and spoken that not everyone is aware of what metrication means, that many people assume that it is simply a change from imperial units to metric units. However, what is really intended is the adoption of the S.I. system of units and this implies much more than just the use of metric dimensions. The two main points of the S.I. system are (i) that every dimension is measured in decimal multiples of a basic unit and (ii) that the system of units is a coherent one. The educational advantages of such a system are too well known to require restating here. Antagonists of change usually point out that time does not conform to condition (i) and while this is true, nevertheless the S.I. system will be a great improvement on our present one and the non-conformity of time should not be used as an excuse for other non-conformities.