The common average montage; Left temporal sharp and slow wave?

Herewith another example:

The above looks a little like a sharp and slow wave at F7-M1-F3-FP1.

Then look at it on the standard AP bipolar montage; see below.

It looks far less conspicuous but nevertheless is best developed on the left on the bipolar montage above. There is a small deflection at F4, which is important.

Then look at it on the coronal montage below.

In the image above, the wave has a large field, primarily centred at CZ and therefore representing a low amplitude vertex wave. This is one of the perils of the common average montage, described in previous posts. Be wary of this montage, especially as you might not recognise waves with a large field.