CC BY-NC-SA does not permit the use of the software for commercial purposes. This violates point 6 of the Open Source Definition[OSD] that says, "No Discrimination Against Fields of Endeavor: The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research."
For example, if the Russian School of Math, or Kumon, wanted to adopt this calculator and software (commercial use, tutoring center), they'd be breaking the license.
This license is a non-starter...
That's right. And prohibiting commercial exploitation violates one of the key clauses of both the Open Source Definition and the Free Software Definition (the part about freedom of use for any purpose). See https://opensource.org/faq#commercial. In other words "open source" doesn't just mean "you can see the source code" (that's known as "visible source" or "source available" software). Rather, "open source" means "meets the Open Source Definition", which is at https://opensource.org/definition.
so the GPL is not open source?
The GPL allows all commercial use. It does not allow proprietary restrictions on redistribution, under certain circumstances, but that's different. You can charge as much money as you want for GPL'd software, and you can base your commercial service on GPL'd software, etc (by the way, this is not just hypothetical -- billions of dollars of commercial activity are based on GPL'd software, including but not limited to the Linux kernel). It's just that when someone receives a copy of GPL'd software from you, you can't place further restrictions on their redistribution -- the permission to redistribute under the GPL comes with the copies. Think of it this way: the GPL prevents monopoly, while permitting commercial use.