Hi Nick,
The point of using the meter was to get a correct exposure as the camera meter can be fooled by the overall area it sees, rather than the light from the face.
Metering from both sides shows the variation, which 'ideally' does not want to be more than 2 stops for portrature, unless you are trying for specific low lighting effects. This is why the reflector was used to bring up the lighting on the side opposite the window.
It would be a good idea for you to photograph an object, or person in similar settings, so that you can see how much the camera differs from the setting shown by the hand held meter if you have one. Possibly another way to do this without a meter is to take a reading as close as possible to the subject, filling the frame. Then step back to normal shooting position and take the reading again. You will find that there is a difference, but you can still take the two shots, one using the aperture value shown by the camera in normal shooting position and the second in manual mode, using the setting shown from the close up reading. I think you will find that the reading from the close up setting will be more pleasing because it will not be taking in the surrounding area of the subject.
I hope that is not too much information for you. Get out the camera and try it out.
The second video will expand on this using flash lighting.
Malcolm