Derive a single reading value based from one datum the nearest before a specific time and one the nearest after.
Calculate the difference between two reading values on two dates, using the
CalcualtedAt style of deriving the start and end readings.
Find the difference between two datum that are nearest in time and within two dates.
Find the difference between two datum that are nearest in time on or before two dates, constrained by a maximum time tolerance.
Find the difference between two datum that are nearest in time on or before two dates, without any limits on how near to those dates the datum are.
An enumeration of supported datum reading type names.