Hello, I’m wondering if there’s a method to show the phase angle difference between two PMUs on Grafana?

I can get the two angles (PMU 1 and PMU 2) to plot on the one panel, but I don’t seem to be able to apply the Subtract function to subtract one angle from the other?

Read the following steps:

```
# GSF Grafana Functions
The Grafana interfaces defined in the Grid Solutions Framework allow for aggregation and operational functions on a per-series and per-group basis. The following defines the [available functions](#available-functions) and [group operations](#group-operations) that are available for a data source implementing the GSF Grafana interface, e.g., [openHistorian](https://github.com/GridProtectionAlliance/openHistorian). Note that any data source that implements the [GrafanaDataSourceBase](https://github.com/GridProtectionAlliance/gsf/blob/master/Source/Libraries/Adapters/GrafanaAdapters/GrafanaDataSourceBase.cs) class will automatically inherit this functionality.
## Series Functions
Various functions are available that can be applied to each series that come from a specified expression, see full list of [available functions](#available-functions) below. Series expressions can be an individual listing of point tag names, Guids or measurement keys separated by semi-colons - or - a [filter expression](https://github.com/GridProtectionAlliance/gsf/blob/master/Source/Documentation/FilterExpressions.md) that will select several series at once. Filter expressions and individual points, with or without functions, may be selected simultaneously when separated with semi-colons:
* Example: `PPA:15; STAT:20; SetSum(Count(PPA:8; PPA:9; PPA:10)); FILTER ActiveMeasurements WHERE SignalType IN ('IPHA', 'VPHA'); Range(PPA:99; Sum(FILTER ActiveMeasurements WHERE SignalType = 'FREQ'; STAT:12))`
Many series functions have parameters that can be required or optional – optional values will always define a default state. Parameter values must be a constant value or, where applicable, a named target available from the expression. Named targets are intended to work with group operations, i.e., [Set](#set) or [Slice](#slice), since group operations provide access to multiple series values from within a single series. The actual value used for a named target parameter will be the first encountered value for the target series – in the case of slice group operations, this will be the first value encountered in each slice. Named target parameters can optionally specify multiple fall-back series and one final default constant value each separated by a semi-colon to use when the named target series is not available, e.g.: `SliceSubtract(1, T1;T2;5.5, T1;T2;T3)`
To better understand named targets, follow these example steps:
1. The following expression produces two unwrapped voltage phase angle series:
[`UnwrapAngle(DOM_GPLAINS-BUS1:VH; TVA_SHELBY-BUS1:VH)`](#unwrapangle)
2. Values from one of the series can now be substracted from values in both of the series at every 1/30 of a second slice:
```

This file has been truncated. show original