It all started, I think, in the basic or advanced forum in a particular thread where someone stated that all tissues should be offgassing when ascending. Others argued that, no, some tissues (TC's) might still be ongassing. I thought it might be neat to display the TC pressures for various segments of a dive. Showing the data suggested a table format and Excel was perfect for that. From there, I kept thinking of things I could add that would make the ss more useful and so I added other sheets.
After the ss grew and became more useful (especially with this last version) I thought, should I charge for it? I quickly decided to offer it free of charge. The problem with charging a fee is that it would require me to give it a higher priority that I might not be able to provide. Don't get me wrong, any complaints or problems I'll look into and try my best to fix but I'm not on the "hook" as I would be if I charged for it. The source code would be locked. One advantage of making it free and open source is that others can look at it and fix problems or enhance it in a way I might not think of. So, creating and maintaining the ss has turned into a hobby that I enjoy very much.
The current version was built from prior versions but not from any other application. The current version's (v20.0) DIVE sheet represents a dramatic departure over earlier versions as it includes support for technical dives and fixed a long-standing problem with calculating NDL times. None of the earlier versions were posted in the technical forum because those versions only supported recreational diving.
You ask if it conforms to ZHL16-C which I take that to mean does it use the half times and m-values that can be found in documentation. The answer is a resounding yes. Or, if what you're asking is if it conforms to the results of certain algorithms and programs I'll let you be the judge of that. The ss will calculate profiles using either Buhlmann table A, B, or C selected from the common parameters. If you want to compare different tables you need to create two copies of the ss with different filenames and then open each file in Excel. For the same profile parameters select different tables in each of the ss's and compare the results. My own testing revealed very little difference between the tables. The NDL's I looked at didn't vary by more that a few minutes.