Calcu-pen (1975)

Sadly for you, someone has already bought this rare Calcupen from Japan. But there's always another. From the Vintage Calculators Web Museum, which reports that it received weak reviews back in '75:

The Calcu-pen is a very unique calculator from the 1975 to 1977 time-frame. One of the earliest ads from 1975 shows the Phenix International company of Wayne, New Jersey (USA) selling the Calcu-pen for $79.95. Ads in Scientific American from early 1977 show the price as low as $19.95. The actual manufacturer is not known and is not present on any of the currently-known printed materials for the calculator (such as sales ads and operating manual). The back cover of the operating manual has a guarantee with returns to be sent to Tru-phonic Sound company of Bellwood, Illinois (USA), but that may have just been one US distributor or servicing agent. An LCD version of a Calcu-pen (with the same spelling) was made in 1981 by Satolex, an Asian company. There may be a connection.

Here it is on video:https://www.youtube.com/watch?v=9suq47-AM1M