ev=log2( ISO) - log2(T) +log√2( f )
Or was that not what you were looking for.

Welcome and pardon my humor. You have it pretty good there. Using the Pen as a guide is a good start. A better one would be to find a light meter. You can find an old Sekonic. Even if the photo cell does not work the slide rule dial can help get you a custom to shutter/aperture combinations.