There are some times when you just want to know that your code worked. And then there are others where, if there's an error, it tells you in NO uncertain terms - but waits.
For these reasons I invented the Dingle(tm). It dingles away in some verifiable area of the screen to show you that it has reached this area - and often, that it won't leave!
The code is easy: increment one specific location on the screen for the user. That will cycle through all the different ASCII codes for that location; and it doesn't matter whether you're using a Virtual Machine or Real Hardware: the location will update!