The format of the file written by the forward model (i.e.the <code>RESULT_FILE</code>) and read by ERT. 
The alternatives are:
<dl>
<dt>ASCII
<dd>A text file with formatted numbers.
<dt>BINARY_FLOAT
<dd>A vector of binary float numbers.
<dt>BINARY_DOUBLE
<dd>A vector of binary double numbers.
</dl>