A neat little trick that I learned to do that is to get a .10 density filter from Kodak and with a spot meter on a tripod aim it at a constant light source and taking a unexposed DEVELOPED neg with the 010 filter sandwiched on it make a reading. there is your .010 above fb+fog. It is great for finding a working speed for your film doing the zone one test. A bit crude yes but it will bring you very close to where you need to be for a fraction of the cost and a real time saver due to the simplicity factor.