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# Persistence
# Introduction
Persistence blocks enable access to and manipulation of historical data stored by the default persistence service. For more information on persistence, the default service, and its configuration see the persistence documentation (opens new window).
The date-blocks shown in this section are described previously in Date handling blocks (opens new window).
# Overview of the Persistence blocks
# Persistence Blocks
Persistence blocks enable access of historical data stored by the default persistence service. For more information on persistence, the default service, and its configuration see the persistence documentation (opens new window).
The date-blocks shown in this section are described previously in Date handling blocks (opens new window).
More about that topic can be viewed at 
Using Persistence data (opens new window)
# Get statistical value of an item
Function: computes any of the below functions for the given item since the time provided by ZonedDateTime-Block
- average: gets the average value of the State of a persisted Item since a certain point in time. This method uses a time-weighted average calculation
- delta: gets the difference in value of the State of a given Item since a certain point in time
- deviation: gets the standard deviation of the state of the given Item since a certain point in time
- variance: gets the variance of the state of the given item since a certain point in time
- evolution rate: gets the evolution rate of the state of the given Item in percent since a certain point in time (may be positive or negative)
- minimum: gets the minimum value of the State of the given Item since a certain point in time
- maximum: gets the maximum value of the State of the given Item since a certain point in time
- maximum: gets the sum of the State of the given Item since a certain point in time
Note: in case no or 0 values are retrieved, make sure that the item in question is actually persisted.
# Check item change / update since a point in time
Function: checks if an item was updated or changed since a certain point in time
Type: boolean true or false
# Provide last updated date of an Item
Function: Provides the last updated date (including time) of an Item Type: ZonedDateTime