Mike? Who's Mike? Lol!
Thanks for the info people, I just found the tabs mentioned (I thought they were part of the construction holding the camera together!). I see the three apertures and the 'B' setting works.
For those interested it has two viewfinders, one on top for 'portrait' layout and one on the side for 'landscape'.
I figure I'll get some FP4 to try it out. I think the camera was made around 1916, as that is the last Patent date stamped on the inner chassis. Before I use it I'll have to sort out some light seal, but that's an easy job.