The value in terms of arc of the scale of the record can be obtained by measuring the distance between the magnet mirror and the recording drum, and in most observations it is such that a millimetre on the record represents one minute of arc. The time scale ordinarily employed is 15 mm.
00005 C.G.S., the time scale being the same as that employed in the case of the declination.
3, where the total flow for the driest year measures too on the vertical percentage scale; the horizontal time scale being divided into calendar months.
That described requires a diagram revolving once in a few hours, otherwise the time scale will be too close; but the ordinary diagram revolving once in 24 hours is often used quite effectively in night inspections by only closing those stop-cocks which are actually passing water.