The Langdon Acme Miter Box was available in three sizes and came with a specially made Disston handsaw. The least expensive model cost $10; the most expensive $14.50.
Standard miter boxes of the day could cut 0 to 45 degrees. The New Langdon Miter Box Improved could cut 0 to 75 degrees. How? Look closely at the right hand fence and you’ll see an adjustable piece that pushes the material away from the fence so that when you swing the saw to 45 degrees you’re actually cutting 75 degrees. That round thing behind the fence is the lock knob. Okay smart guys at the power tool companies – why aren’t you doing this with miter saws?
The notes below this Langdon Adjustable Miter Box say that if you send them your saw the company will fit it to the miter box for free. But they’ll charge you if the saw’s messed up and they have to fix it. It sounds reasonable to me.