LABSAMPLING

The LABSAMPLING modifier affects the calculation modes that interpolate a value at the start of each interval. Instead of using interpolation, lab sampling is used. When querying highly compressed data you may have intervals with no raw samples stored. An average from 2 P.M to 6 P.M on a one hour interval will interpolate a value at 2 P.M., 3 P.M., 4 P.M, and 5 P.M and use those in addition to any stored samples to compute averages. When you specify LABSAMPLING, then lab sampling mode is used instead of interpolated sampling mode to determine the 2 P.M., 3 P.M., 4 P.M., and 5 P.M., values.

A lab sampled average would be used when querying a tag that never ramps but changes in a step pattern such as a state value or setpoint.

Note: Use the LABSAMPLING modifier with calculation modes only, not raw or sampled retrieval like interpolated modes.
Example

Import this data to demonstrate the behavior of the LABSAMPLING query modifier. 

[Tags]
Tagname,DataType,HiEngineeringUnits,LoEngineeringUnits
RAMPUP,SingleFloat,100,0
[Data]
Tagname,TimeStamp, Value,DataQuality
RAMPUP,06-Aug-2012 9:01:00.000,1,Good
RAMPUP,06-Aug-2012 9:02:00.000,2,Good
RAMPUP,06-Aug-2012 9:03:00.000,3,Good
RAMPUP,06-Aug-2012 9:04:00.000,4,Good
RAMPUP,06-Aug-2012 9:05:00.000,5,Good
RAMPUP,06-Aug-2012 9:06:00.000,6,Good

Run this query without a modifier to see the minimum values using the interpolated values: 

set starttime='06-Aug-2012 09:02:30',endtime='06-Aug-2012 09:05:30' 
select timestamp,value,quality
from ihrawdata
where tagname = RAMPUP and samplingmode=Calculated and CalculationMode=minimum and numberofsamples=3
Time StampValueQuality
8/6/2012 09:03:302.500000000000100.0000000
8/6/2012 09:04:303.500000000000100.0000000
8/6/2012 09:05:304.500000000000100.0000000
The returned minimum values are stored values but sampled forward to each interval timestamp. This is the behavior of lab sampling and is applied here to calculated values.
Anticipated Usage

Use the LABSAMPLING modifier to query the minimum, maximum, and average values of tags that change in a step fashion and never ramp. For example, you may want to retrieve the minimum of a set point. This tag would change from one value directly to another without ramping. And the value may not change in a long period. A minimum should not return a value that ramps over a long period of time from one set point value to the next. The LABSAMPLING modifier is useful for Calculation modes and not the Sampling modes.