**Syntax**

` >>>> LOGARITHM`

**Parent Command**

all third-level commands in block` > OBSERVATION`

**Subcommand**

` - `

**Description**

This command takes the natural logarithm of an observable variable. The corresponding measurement error is assumed to be log-normally distributed. Taking the logarithm is suggested when the observation assumes values over many orders of magnitude (e.g., concentration, water potential). Note that this option emphasizes the importance of smaller values of the variable, and is not applicable to data sets that contain zero measurements.

Taking the natural logarithm is a special case of the Box-Cox transformation with parameter *lambda* set to zero.

**Example**

` > OBSERVATION
>> CAPILLARY PRESSURE
>>> ELEMENT: TP__1
>>>> first take the ABSOLUTE value and
>>>> then the LOGARITHM
>>>> standard DEVIATION of untransformed data: 1.0E4
>>>> DATA on FILE: wp.dat
<<<<
<<<
<<`

**See Also**

` >>>> BOX-COX `