Copal shutter f markings

A dumb question from a newcomer to the joys of large format. I've recently acquired a Schneider Tele-Xenar f 5.5 240 mm for a 4x5 wooden field camera. The Copal No. 1 shutter does not have f markings, though there is a blank tab where these would normally be. The brochures I've scoured suggest Copal shutters never have these markings, and don't have the automatic attachments of Compur shutters. And unlike the Compur, the Copal does not have click divisions on the f lever. Could someone tell me what is the easy way to work out the various f stops? Many thanks. Jonathan Manthorpe, Hong Kong.

Generally the lens manufacturer supplies a plate which is calibrated

to show the right f-stops for the lens - since any number of

different lenses can come in a copal 1 shutter. Your lens may

have been remounted in the shutter. You can probably work out

approximate f-stops by measuring the iris opening as seen from

the front of the lens - full open is f/5.5, when the iris opening

is half of full, that's f/11, and so on.