Collection Item 

Casio 121F
Brand:  Casio. 
Model:  121F. 
Origin:  Japan. 
Introduction:  1975, this example was built in 1976. 
Type:  Basic desktop calculator with VFD display. Operates only with AC power and has a multivoltage selector for US or European norm (110v, 117v, 220v and 240v). 
Functions:  4Basic function plus Square Root, Percent, constant, memory. 
Display:  One blue VFD glass tube with 12 digit plus one position for Memory, Negative and Overflow indication at the far left of the display. Numerals have a rare 8segment layout, instead 7 segments. The 8nd. segment is used only for the digit 4. Also, each numeral have a decimal point separator (bottom right) and thousands separator (on the top left). 
Keyboard:  23 reedlike keys plus 3 sliding switches for Constant On/Off, Round mode and Decimal Point selection. Also an On/Off switch. 
Main chips:  NEC PD286C without datecode plus 2 Toshiba TM4352P with datecode 6C (March 1976). 
Logic comments:  Pseudo RPN notation, very used during the seventies. For example: To compute 2+3 you must enter 2 += 3 +=. For 53 you must type 5 += 3 =. Memory operates with the standard M+, M, MR and MC keys and there is an indicator M on the display when memory content is not zero. Overflow or dividebyzero condition is indicated by a big dot on the display and is not recoverable. Constant is only for multiply and divide, not for add or subtract. Negative square root is allowed but is displayed with the same sign, for example: Square Root of 2 gives 1.4142... There is no 0 bug or ghost decimal point bug. 
Remarks:  Low profile robust desktop calculator with beauty design and very readable display. 
Size:  8.66 x 6.89 x 2.24 in, 220 x 175 x 57 mm. 
Condition:  (8/10) Very Good, working. 