Time interval between measurement start points.
The interval between consecutive measurement start points is stated in
the same units as the file time axis, (fractional) days.
averaged data the interval is 1/24 = 0.041667, for
daily averaged data it is 1, for weekly data 7, etc. Stating this interval implies that it
applies for the whole data section of the file. Please use a precision of at least 6 digits
right of the decimal point for real numbers.
For irregular data this value is set to 0.