This particular error was extremely unlikely to happen upon by chance, and it was distributed as an interesting fact with careful directions on how to get the error. They all graph elementary functions with features for analysis. Generally, more money buys more features and finer display. Your primary need for having a graphing calculator is convenience. Features are nice if you have the money, but there is no need to have the most expensive, powerful model.
All brands allow programming.
For more information see Graphics Calculator Programming . Really, I do like them all. The HP 38G is not a stack calculator like traditional HP's, so it should be familiar to people who have used scientific caluclators. The fancy features are there, yet the practical features are up front. I am not a professional evaluator of technology, just a user with impressions to share.