HP 35

HP 35

This HP 35 was the first scientific pocket calculator and was introduced in 1972.  It stayed in production until 1975 and retailed at a price of $395.00. The 35 was allegedly a hack by an HP engineer of the HP 9100 which was a large desktop calculator with a price of over $1000.00. The engineer shrunk the 9100 down and incorporated a number of trigonometric and exponential functions that no other “pocket” calculator. In fact, all pocket calculators at the time were just four function calculators.

Other engineers at HP liked the 12 prototypes that were built so HP decided to make it a full fledged product. It was named the HP-35 because it has 35 keys. Early versions of the 35 only had the Hewlett Packard name on the faceplate but later versions added “35” to the name. It took two years and about one million dollars to develop.

HP 35 Case

The HP-35 utilizes a 15 digit LED display that would illuminate each LED segment separately as opposed to the entire digit. It is 5.8 inches long and 3.2 inches wide which is just right to fit in a shirt pocket. HP didn’t originally feel that there was enough demand to produce the calculator at the nearly $400.00 price point. But, in just the first year they sold over 100,000 units and sold over 300,000 during its production life. HP even made the HP 35s in 2007 which is a retro model paying homage to the original 35.

HP 35 Battery Compartment

Obviously Bill Hewlett’s vision and ability to go against conventional marketing wisdom at the time led to a revolution in calculating that is still with us today.

One bug in early HP-35’s was 2.02 ln e^x which gave the result 2 as opposed to the correct 2.02. 25,000 35’s had been sold by that time and HP offered those customers replacements of which only about 25% returned theirs.

HP 35 Main Board

As I mentioned before there were basically four production differences over the life of the 35. The first production run had a small red dot to the right of the on/off switch that would show when the calculator was turned on and did not have the “35” designation on the label.

The second version got rid of the red dot.  The third version had the “35” designation. The fourth version had all the function notation molded into the keys as opposed to printed on the calculator body. The list below shows the 4 production variations as well as two prototype versions.

HP 35 Label
  • Prototype version 1: beige case, no label, yellow keys for basic functions.
  • Prototype version 2: same as first version except with a black case.
  • Production Version 1: no “35” designation, small red dot, letters on the face .
  • Production Version 2: no “35” designation, no red dot, letters on face.
  • Production Version 3: added “35” designation, no red dot, letters on face.
  • Production Version 4: “35” designation, no red dot, letters molded into keys.
HP Prototype
HP 35 Red Dot

Obviously the prototypes are nearly impossible to find.  The first version with the red dot is very difficult to find as well so if you see one scoop it up. The others aren’t too difficult to find since so many were made and built to last. The red dot version sells for upward of $1000.00 in excellent functioning condition while the rest sell for around $75.00 to $300.00 depending upon the accessories included.

Right Now on eBay 
Clicking a link to eBay may result in a referral commission being paid if a purchase is made.

One thought on “HP 35

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.