How do you put calculator on dock

Care to share which OS you are using?

Calculator has always been pre-installed in my Dock ever since Apple invented the Dock. The original calculator app is inside the Application folder. Drag the original app to the Dock. The original app will move back to the App folder & a duplicate calculator app will be sitting in your Dock.

I'm using El Capitan ver. 10.12.2 and I had the same problem. I knew the procedure of going to my hard drive, clicking Applications, finding the app and dragging it to the dock, however, I could not locate my hard drive (it was not where it used to be in the earlier version of the OS I had). So, I started looking around. There was an Icon on my dock that looks like a rocket inside a circle and it's blasting off at about a 1 o'clock trajectory. I click on the rocket. A window appeared and as it turns out, that rocket icon stands for "Launch Pad". Funny, right? So inside that window, to what do my wondering eyes appear? A panoply of icons, and lo and behold there was Calculator! I dragged it to my dock, and just like Baby Boomer said, a copy stayed in Launch Pad and the Calculator entered my dock - problem solved.