Understand retrieval mode

You can choose to see average, minimum, maximum, last, or sum data values.

• Average
  When you choose to view the Average for your data, AVEVA Historian Client Web uses a time-weighted average algorithm to calculate each data value shown.

  With Average, values are multiplied by the time difference between the points to determine the time-weighted value. So, the longer a data tag had a particular value, the more weight that value holds in the overall average. The overall average is determined by adding all of the time-weighted values and then dividing that number by the total amount of time.

  For the following data values of a tag that uses linear interpolation, the time-weighted average is computed as:

  (((P1 + P2) / 2) x (T2 - T1)) + (((P2 + P3) / 2) x (T3 - T2)) + (((P3 + P4) / 2) x (T4 - T3)) / (T4 - T1) = Average

  

  If the same data tag uses stair-step interpolation, the time-weighted average is:

  ((P1 x (T2 - T1)) + (P2 x (T3 - T2)) + (P3 x (T4 - T3))) / (T4 - T1) = Average

• Maximum
  When you choose to view the Maximum for your data, AVEVA Historian Client Web shows the maximum value from the actual data values within a retrieval cycle. If there are no actual data points stored on the historian for a given cycle, nothing is returned. NULL is returned if the cycle contains one or more NULL values.

  The number of cycles is based on the specified resolution or cycle count. However, maximum retrieval is not a true cyclic mode. Apart from the initial value, all points returned are delta points.

  Maximum retrieval only works with analog data. For all other data, normal delta results are returned.

• Minimum
  When you choose to view the Minimum for your data, AVEVA Historian Client Web shows the minimum value from the actual data values within a retrieval cycle. If there are no actual data points stored on the historian for a given cycle, nothing is returned. NULL is returned if the cycle contains one or more NULL values.

  The number of cycles is based on the specified resolution or cycle count. However, minimum retrieval is not a true cyclic mode. Apart from the initial value, all points returned are delta points.

  Minimum retrieval only works with analog data. For all other data, normal delta results are returned.

• Last
  When you choose to view the Last for your data, Insight shows the final data value recorded for the timeframe you specify.

• Total
  When you choose to view the Total for your data, AVEVA Historian Client Web uses a integral algorithm to calculate each data value shown.

  The total equals the time-weighted average multiplied by the total amount of time in the given timeframe. For example, if the time-weighted average for a tag during a 1-minute cycle is 3.5 liters per second, the total (calculated by the integral retrieval mode) is 210 for that cycle (3.5 liters per second multiplied by 60 seconds).

• Meter
  When you choose to view the Meter for your data, AVEVA Historian Client Web gives you the total counted units for this tag from the beginning to the end of the time period.