https://www.ryanheise.com/cube/heise_method.html
But the site is now defunc and offline. As I had been practicing it extensively that spelled trouble. But fortunately I was able to mirror the site locally and was able to run it.
Here's the mirror of the site. Not all links will work, but most of those will. All the relevant pages should work.
Enter the mirror of the site here :
https://cube.habibur.com/ryans/