Series Type setting completely change the style of how "raw" source values are converted to chart data points. There are four series types:
| • | Gauge |
| • | Counter |
| • | Derive |
| • | Absolute |
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If the series is based on statistics, its type must match the type of statistical channel it's based on. |
Gauge
The source value is kept as-is, without any conversion. This is a default setting that is suitable for most cases.
This type is suitable for simple metering like temperature, number of people in the room or stock price.
Counter
Suitable for continuous incrementing counters. The Counter-type data source assumes that the counter never decreases, except when a counter overflows. The series takes the overflow into account. The counter is stored as a per-second rate. When the counter overflows, series checks if the overflow happened at the 32bit or 64bit border and acts accordingly by adding an appropriate value to the result.
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Simply speaking, Counter will look at the difference between the previous value and the current value (the delta). An example would be an odometer. The chart data point is computed as: delta(counter) divided by delta(time). |
Derive
Derive-type series will store the derivative of the line going from the last to the current value of the data source. This can be useful for gauges, for example, to measure the rate of people entering or leaving a room. Internally, derive works exactly like Counter but without overflow checks. So if your counter does not reset at 32 or 64 bit you might want to use Derive and combine it with a Minimum Value of 0.
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Derive is similar to Counter, but now it can also go back. An example could be something monitoring a bidirectional pump. The resulting rate can be negative as well as positive. |
Absolute
Absolute series are used for counters which get reset upon reading. This is used for fast counters which tend to overflow. So instead of reading them normally you reset them after every read to make sure you have a maximum time available before the next overflow. Another usage is for things you count like number of messages since the last update.
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Absolute series is also similar to the odometer, but here the counter is reset every time it is read. Chart data point computed as: value divided by delta(time). |