-mag:
When the vertical and horizontal sizes are converted and this is not specified, the value of \magstep written in the dvi file is used (Property Sheets->[Resolution]).
If \magstep is m, the size is 1.2^m times. A font resolution is searched for as a conversion that corresponds to this value.
The magstep values of 0, 1,..., 9 can be specified in the parameter file. A "-1" indicates the default. The "magstep half" specifies "-half=+".
Regardless of the current state, the default is always displayed on the [Resolution] in Property Sheets. (Erroneously setting a special magstep at start-up is prevented.) The current mag value can be found by "Help -> Information".