Which would put the $600 Popular Science Magazine calculator ad at 1971 or 1972.
"Hewlett-Packard Corporation joined the market in early 1972 with the
HP-35 scientific calculator. It could not only add, subtract, multiply, and divide but compute trigonometric functions, logarithms, and exponents. In other words, it did the work of a slide rule and more. The calculator sold for $395. Not to be outdone, Texas Instruments introduced its first calculator, the Datamath (or
TI-2500), later that year. The device carried out basic arithmetic and sold for $149.95." (
Electronic Calculators—Handheld )
So within a year of seeing the ad there were calculators at about half and one-fourth the $600 price tag. 1973 saw the
SR-10 for $150 came out.
What followed was a race to put in as many features possible while at the same time reducing the price.
Being born in 1966 I saw first hand the insane progression of digital devices of the 1970s and 1980s.
In fact, early on the school I was in forbid the use of digital calculators but my parents had old text books from the early 1960s which included how to use a slide rule and so I brought my father's.
The funny thing is that many of my math teachers didn't know what to do as the rule referred to a
digital calculator which a slide rule was most definitely wasn't. More over the other kids didn't even know how to use one.
Around the 8th grade the school gave up and allowed digital calculators. My high school not only allowed calculators but had a computer room (filled with Apple IIs). The middle school is long gone replaced by the
A Plus Arts Academy and my high school now calls itself Eastmoor Academy High School.