Take a look at this great article titled "Long Live the HP-16C" by Valentin Albillo here.
Love this device! Of course, the HP Museum site has useful information about this and many other HP calculators. If seeking the missing manual, there is a scanned version here.
Also, Cameron Paine has a faithful simulation running on the Windows OS here. (Select the menu item View...Classic for the nostalgic visual replica.) Another version for the browser is meh.
Update 20150227:
One Voyager was not enough! We added a near-flawless HP-11C.
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