So far, we have introduced the manual analysis of
analogue “stripchart” records. Most analyses are
performed by computer for which digital records are
used, i.e. the vertical displacement of the ocean surface
(or the position of the pen at the chart recorder) is given
with a sampling rate of 1–10 times per second (1–10
Hz). For example, a record of 20 minutes duration with a
sampling rate of 4 Hz contains 4 800 values.