Reverse notation calculator is a mathematical notation where every operator follows all of its operands. It is also known as Postfix notation and is parenthesis-free.

The Reverse notation scheme was proposed in the early 1960s to reduce computer memory access and utilize the stack to evaluate expressions. The notation and algorithms for this scheme were enriched by Australian philosopher and computer scientist Charles Hamblin in the mid-1960s.

In Reverse notation, the operators follow their operands; for instance, to add three and four, you would write "3 4 +" rather than "3 + 4". If there are multiple operations, the operator is given immediately after its second operand; so the expression written "3 − 4 + 5" in conventional infix notation would be written "3 4 − 5 +" in Reverse notation: first subtract 4 from 3, then add 5 to that. An advantage of Reverse notation is that it obviates the need for parentheses that are required by infix. While "3 − 4 * 5" can also be written "3 − (4 * 5)", that means something quite different from "(3 − 4) * 5", and only the parentheses disambiguate the two meanings. In postfix, the former would be written "3 4 5 * −", which unambiguously means "3 (4 5 *) −".

Interpreters of Reverse notation are often stack-based; that is, operands are pushed onto a stack, and when an operation is performed, its operands are popped from a stack and its result pushed back on. Therefore, Stacks (or Reverse notation), have the advantage of being easy to implement and very fast.

Back in college, I forgot my calculator for a calculus exam. My professor said I could borrow his. He warned me that it was a reverse notation calculator. I didn't know what that meant, and thought a calculator is a calculator. Well, it didn't take long for me to find out that I was dealing with a whole other animal. I couldn't add 1 + 1 with this thing, much less the complex equations I needed it for this exam. Panicing, and embarrased that I didn't know how to use his "calculator", I had to get up again and ask him some questions on how to use it. I already felt I was being needy for using his calculator, and having to ask him how to use it made me feel even more needy. He was very generous, and gave me a quick 5 minute lesson on how it worked. I went back to my desk, and slowly got through my exam. I ended up running out of time because of the learning curve of using the new calculator. But at the end, I was realizing the potential of what this type of calculator had over my conventional calculator. I ran to the bookstore, and bought this new "Reverse Notation" calculator by HP. I became faster at using it, and I was eventually able to do my homework a lot faster, and my grades in calculus got a lot better. Then the day came, when a friend of mine asked if he could borrow my calculator. I smiled, and said sure, but warned him it was reverse notation. He just say ya, ya, it's a calculator... I know how to use a calculator. So I handed it to him, and watched with a smile as he attemped to add and subtract like he did on his calculator. He shortly gave up, and gave it back to me, frustrated that he couldn't use it, and told me it was broke. I tried to explain how it worked, and the benifits he would get out of it, but he just turned around and asked the guy on the other side if he could borrow his "normal" calculator. These are the same struggles people today are having using a Revit technology software package. Some people are willing to make the change and see the benefits. It's difficult to describe the benefits of a reverse notation calculator, but once you use it, it becomes apparent. It's the same with Revit.

Comparing Revit to AutoCAD is similar to comparing Reverse Notation calculator to a traditional calculator. They both can get you similar results, but getting there is totally different. Revit is purposed based to be advantageous for model building, and has tools in it built to make modeling faster and easier than traditional AutoCAD.

When handed a Reverse notation calculator (Revit), you might say that you know how to use a "calculator" (CAD). But when you try to add 3 + 4 like you did in your traditional calculator (AutoCAD), you won't get the same results, and it can be frustrating.

You might also say that on the surface, they both look the same, and can do similar things, so why would I want to use this other calculator (Revit software)? Because its when you get to the more complex stacked based operands that you really see the advantages of the reverse notation. It's the same with Revit, where you really see the advantages of the parametric relationships of the model.

People who learn how to use a Reverse notation calculator can enter more complex calculations, and can enter those calculations in faster. People who learn how to use this type of calculator never go back to using a traditional calculator. The same can be said about Revit. Those who learn how to use Revit, never go ack to using traditional AutoCAD.

An example of this is my friend Todd Shackelford, writer of the Lazy Drafter Blog, just recently shut down his AutoCAD blog because he doesn't use AutoCAD anymore. A trend that is becoming more familiar. He is concentrating on his other blog, CAD Shack which is dedicated to Revit and BIM processes. Another trend that is becoming more familiar.

So when you do start using a Revit based program, and it seems complicated, don't say, "well, this is stupid. I can do this in AutoCAD." Because in short, you are probably right, you can. But once you learn how to do it correctly in Revit, you will be able to do it faster and easier than you could in AutoCAD.

Thanks for this great comparison. I love my reverse notation HP and the benefits of that calculator. when talking with people who use revit it's very apparent who understands "what" revit is and who thinks revit is just 3d CAD.

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