[Accumulator]¶

As LOOP packets arrive, WeeWX holds the values for each observation type in an accumulator. At the end of the archive interval the accumulator is asked for one value per type, and those values become the archive record.

How that happens is settable per observation type. The defaults suit the types WeeWX knows about: temperatures are averaged over the interval, rain is totalled, txBatteryStatus reports its last reading. A type WeeWX has not seen before, one that your driver or a service adds, is averaged. That is wrong for anything that counts or accumulates.

This section is not in the distributed weewx.conf. Add it only for the types whose treatment you need to change:

[Accumulator]
    [[lightning_strike_count]]
        extractor = sum
    [[lightning_distance]]
        extractor = min

Each subsection is named after an observation type and takes any of four options. Nothing else needs to be given: what you leave out keeps its default.

The values each option accepts are listed below. For how the accumulators work and what they do between one packet and the next, see Accumulators in the wiki.

Note

An unrecognized value raises a KeyError naming it, rather than a message saying what is wrong. It is not raised at startup either, but the first time the type turns up in a packet, or at the end of the first archive interval. The names below are the whole of what is accepted.

accumulator¶

Which kind of accumulator to use, and therefore what it is able to remember.

Value	Keeps
`scalar`	Sum, count, first, last, minimum and maximum, with their times
`vector`	As `scalar`, plus direction. Used by `wind`
`firstlast`	The first and last value only. The only one that accepts strings

Default is scalar. Use firstlast for a type whose values are text: the others do arithmetic on what they are given.

adder¶

What to do with each value as it arrives.

Value	Effect
`add`	Add the value to the accumulator
`add_wind`	Add a wind speed, keeping direction and gust with it
`check_units`	Do not accumulate; check that the unit system has not changed
`noop`	Discard the value

Default is add. The other three exist for windSpeed, usUnits and dateTime respectively, and are unlikely to be useful elsewhere.

merger¶

What to do when the finished accumulator is merged into the daily summaries at the end of the interval.

Value	Effect
`minmax`	Keep the lowest minimum and the highest maximum
`avg`	Keep the lowest minimum, but use the average as the maximum

Default is minmax. Use avg if you have set loop_hilo to False.

extractor¶

What the accumulator contributes to the archive record. This is the option you are most likely to want.

Value	Puts into the record
`avg`	The average over the interval
`sum`	The total. `None` if nothing arrived, rather than zero
`min`	The lowest value seen
`max`	The highest value seen
`first`	The first value seen
`last`	The last value seen
`count`	How many values arrived
`wind`	Fans out into `windSpeed`, `windDir`, `windGust` and `windGustDir`
`noop`	Nothing. The type does not reach the archive record

Default is avg.

Which one to pick follows from what the number means. A reading taken at a moment, such as temperature or pressure, averages. Something counted during the interval, such as rainfall or lightning strikes, sums. A running total that the hardware maintains, such as dayRain, takes last: adding those up would count the same rain many times over. A status or a serial number takes last too.

A text field needs both options. Averaging is impossible for it, so say which accumulator to use as well as what to extract:

[Accumulator]
    [[forecastText]]
        accumulator = firstlast
        extractor = last

The settings WeeWX ships with are at the top of weewx/accum.py, and are worth reading before overriding one. Whether the accumulator is asked for a record at all depends on record_generation in [StdArchive].