Monroe Calculating Machine

Does anyone know where I can find out more about this old mechanical calculator? http://www.jarai.org/temp/monroe/0830_001-sm.jpg http://www.jarai.org/temp/monroe/0830_002-sm.jpg http://www.jarai.org/temp/monroe/0830_003-sm.jpg The unit is fully operational. With some inspiration from the Curta instruction manual, I've been able to figure out addition, subtraction, multiplication, and division on this device. I picked it up at a local yard sale today for a reasonable $30. So far, I've not been able to find much about this particular model. Most everything I can find talks about Monroe's later electromechanical calculators. The closest match I found is this one from the Computer Museum in San Diego, but the image is very blurry and there isn't much information about the calculator. http://www.computer-museum.org/collections/monroe_addc.html The next example is this one but it is a bit more streamlined than mine, so I'd guess it's a slightly later model. http://www.officemuseum.com/Monroe_Calculating_Machine_Co._NY_OM.jpg http://www.officemuseum.com/calculating_machines_pinwheel_other.htm The identifying marks on the calculator itself are the "Monroe Calculating Machine Company, New York, U.S.A." on the front and a number stamped in the metal underneath the carriage--41516--which I'm guessing is the serial number. The keyboard keys seem to be made from Bakelite. -brian.