My most recerntly-purchased camera...a 1938 vintage Baby Speed Graphic, the model that shoots two-and-a quarter by three-and-a-quarter inch sheet film. I also have a vintage 6x6 cm rollfilm back for this camera. it has a well-tuned Kalart rangefinder fitted to it.
Determining the speed of the in-body focal plane shutter is done by cross-referencing the Tension Number with the width of the focal plane shutter's moving aperture, or slit. As you can see, there are 24 possible focal plane shutter speeds, ranging from 1/10 second to 1/1000 second. The leaf style shutter that's mounted with the lens offers the "old speeds" of Bulb,Time, and from 1 second to 1/400 second, using the common pre-WW II speeds of 1 second, and fractional speeds of 1/2,1/5,1/10,1/25,1/50,1/100,1/200,and 1/400 second.
Baby's Shadow, iPhone snap, Instagram post I did a while back. 1938 camera from the USA meets 2014 carbon fiber tripod from China.
A close-up detail of the lens and shutter mechanism. Blazing lens speed! An f/4.5 maximum aperture! Here the shutter has been set to T, or Time. One press of the release opens the shutter, and keeps it locked open until the shutter release is pressed a second time; this speed is super-useful for groundglass set-up and focusing, as well as for long, timed exposures made without a locking cable release.