Original racing-based 1971 advertisement for Heuer's 1970s Ref. 110.663 Calculator chronograph, published in a British magazine.
 
"Heuer Doesn't Make Ordinary Watches - Here's the Proof"
 
In 1971, Heuer launched a technical and futuristic (and quite unusual) new model with a mathematical sounding name "Calculator."  With each Calculator came a manual with detailed explanations about all possible arithmetic operations.  
 
Why?  Heuer’s Calculator has a sliderule bezel that allows a sophisticated system to solve difficult arithmetical problems.  
 
The Heuer Calculator was designed for those who wanted a slide rule on their wrist for conducting mathematical calculations.  Today, it’s remarkable for more than just large size and unusual complication – namely, it’s a more approachable price point than other vintage Heuer models.
 
The Heuer, "Calculator, Automatic Chronograph," Ref. 110.633 was an oversized, tonneau-shaped automatic with a following among those seeking highly unique tools of industrial design.  It’s two-layer slide rule on the bezel features a rotating outer ring, with the inner ring remaining fixed in place.  The slide rule is designed to measure distance, but convert weight and volume from the imperial to the metric system (and vice versa).
 
Keeping all slide rule demarcations on the bezel allows the dial to remain uncluttered, retaining a classic 1970s Heuer look, replete with bright neon hands and the subdial markers with a date at six.  Heuer offered the Calculator in a range of references, to include navy blue and black dial options.  Heuer ceased production of the Calculator in 1982.
 
Dimensions: roughly 2 inches wide by 10 inches high