This is Olivetti's Summa Prima Model 20 manual calculator.  It is in very good condition, no scratches or damage to the casing and the mechanics are functioning smoothly. Many examples show signs of ageing and hard use but this one is in excellent condition. Like all of these 1960's calculators they need maintenance with simple lubrication/greasing being the main requirement to keep it running smoothly. It has all of the expected functions of addition, subtraction, multiplication, totalling and the ability to add in account numbers. All key presses are printed on the print roll (absent here) via the typewriter ribbon  in red or black depending on the function. I have been unable to check alignment etc as I do not have a print roll, but there are You Tube videos assisting if required. Access to the mechanism is fairly easy with removal of the casing. After such a long time since everyday use it would no doubt  benefit from an interior clean and lubricate, in case any part of the mechanism is sticking. At the present time it appears to run smoothly and all buttons respond. This is an opportunity to own a classic piece of Italian engineering from the last of the manual calculators, prior to electronics being added. Whilst it may appear complicated to use it is pretty simple in reality and can still be used today as a functioning piece of equipment. Uses extend to financial calculation with the appropriate settings or straightforward calulating functions. This model has the full set of function buttons unlike the majority, especially the  W/N switch.