**Syntax**

` >> DRIFT`

**Parent Command**

` > PARAMETER`

**Subcommand**

` >>> NONE
>>> SET`

**Description**

This command selects as a parameter the slope of a time-dependent trend. The trend is added to the TOUGH2 output referring to a specific data set:

z_{TOUGH2} = z + drift*time

where (drift*time) is the trend added to the calculated TOUGH2 output z_{TOUGH2}. The result z is compared to the measurement z* of the corresponding data set. This option allows removal of a trend in the data (for example, a flowmeter may exhibit an unknown offset and time-dependent trend that needs to be estimated). A non-zero value must be provided as initial guess through the iTOUGH2 input file using command `>>>> GUESS.` The data set is identified by number using command `>>> SET` (p).

**Example**

` > PARAMETER
estimate coefficients of regression dz=A+B*time to correct flowmeter data
>> SHIFT
>>> NONE
>>>> ANNOTATION: coefficient A (constant)
>>>> INDEX : 2 3 4 (identifies data sets)
>>>> GUESS : 4.0E-6 [kg/sec]
<<<<
<<<
>> DRIFT
>>> NONE
>>>> ANNOTATION: coefficient B (slope)
>>>> INDEX : 2 3 4
>>>> GUESS : 1.0E-9 [kg/sec/sec]
<<<<
<<<
<<`

**See Also**

` >> SCALING | >> LAG | >> SHIFT | >>> SET (p)
`