58 THE ANTARCTIC MANUAL, 
should be taken at one time, as waves appear to run in series. The 
more numerous the observations, the more accurate the mean result 
is likely to be. A little practice will make wave timing easy, except 
in a cross or confused sea, which complicates matters. If it be 
desirable to note the rolling of the ship simultaneously with the 
timing of the waves, a third observer will be required for that pur- 
pose, but such a set of observations may very well be taken before 
or after the others. 
In all cases the results obtained can, of course, only be regarded 
as approximate, but when sufficient care has been taken they are 
quite near enough for all practical purposes. 
