Instrumentation/Instrumentation: Update timestamp documentation

doc/instrumentation.rst

@@ -139,6 +139,14 @@ Instrument
    ``<site>_<kind>`` (see :class:`InstrumentChannel`). The order of the columns
    will be the same as the order of channels in ``Instrument.active_channels``.
 
+   If reporting timestamps, one channel must have a ``site`` named ``"timestamp"``
+   and a ``kind`` of a :class:`MeasurmentType` of an appropriate time unit which will
+   be used, if appropriate, during any post processing.
+
+   .. note:: Currently supported time units are seconds, milliseconds and
+             microseconds, other units can also be used if an appropriate
+             conversion is provided.
+
    This returns a :class:`MeasurementCsv` instance associated with the outfile
    that can be used to stream :class:`Measurement`\ s lists (similar to what is
    returned by ``take_measurement()``.
@@ -211,27 +219,31 @@ be reported as "power" in Watts, and never as "pwr" in milliWatts. Currently
 defined measurement types are
 
 
-+-------------+---------+---------------+
++-------------+-------------+---------------+
 | name        | units       | category      |
-+=============+=========+===============+
++=============+=============+===============+
 | time        | seconds     |               |
-+-------------+---------+---------------+
++-------------+-------------+---------------+
+| time        | microseconds|               |
++-------------+-------------+---------------+
+| time        | milliseconds|               |
++-------------+-------------+---------------+
 | temperature | degrees     |               |
-+-------------+---------+---------------+
++-------------+-------------+---------------+
 | power       | watts       | power/energy  |
-+-------------+---------+---------------+
++-------------+-------------+---------------+
 | voltage     | volts       | power/energy  |
-+-------------+---------+---------------+
++-------------+-------------+---------------+
 | current     | amps        | power/energy  |
-+-------------+---------+---------------+
++-------------+-------------+---------------+
 | energy      | joules      | power/energy  |
-+-------------+---------+---------------+
++-------------+-------------+---------------+
 | tx          | bytes       | data transfer |
-+-------------+---------+---------------+
++-------------+-------------+---------------+
 | rx          | bytes       | data transfer |
-+-------------+---------+---------------+
++-------------+-------------+---------------+
 | tx/rx       | bytes       | data transfer |
-+-------------+---------+---------------+
++-------------+-------------+---------------+
 
 
 .. instruments: