# Transforming abiotic variables

Transformations may be appropriate for environmental variables too, though usually for a different reason (e.g. in order to justify using Euclidean distance as a dissimilarity measure on normalised variables).  However, these are usually selective transformations, required only for some variables, and with different transforms potentially applicable to variables of different types. The global **Pre-treatment>Transform (overall)** applies the same simple power or log transform to all variables, whereas **Pre-treatment>Transform (individual)** operates only on highlighted portions (usually sets of variables), and can allow user-defined expressions if a specific formula is appropriate to a certain variable. More sophisticated data manipulations with user-defined expressions are deferred to Section [11](https://learninghub.primer-e.com/books/primer-v7-user-manual-tutorial/chapter/11-general-data-manipulation-tools-further-pre-treatment); here we concentrate on one or two commonly used transforms for abiotic variables.

In the <ins>Ekofisk ws</ins>, the <ins>Ekofisk environmental</ins> sheet holds 9 variables measured on sediments at the same set of 39 sites: total hydrocarbons (THC), several heavy metals, redox and two particle size measures, % mud and $\phi$ mean. The first variable in the sheet is just distance in km from the oil-field centre, not of itself a measure which organisms in the assemblage will respond to, and which should not be used for any assessment of the pattern of environmental change around the field.