Reasons for not indexing a resource
When indexing a puzzle it's important to ask whether a student can connect the puzzle's solution to a mathematical idea they're already familiar with. Just because a puzzle can be analyzed using mathematics, doesn't necessarily mean it's appropriate for students. For example, peg solitaire can be analyzed using group theory to determine the number of unique solutions, but then the puzzle is only appropriate for group theory students. We cannot broadly call the puzzle a mathematical puzzle and give it to a general audience. We must carefully consider who we're giving the puzzle to, and whether they have the necessary prereqs to solve it.
Webpages with horrible background colors
Here's a perfect example.
Videos without dialogue
Sometimes a video is made without any dialogue, such as this one. Clearly, a written article is superior in this case.
I won't index promotional videos, like this one. I think Eddie Woo is one of the best teachers out there, but some of his videos have very little educational value. These videos are usually promoting a book or otherwise getting his name out there.
I won't be indexing channel intro videos, like this one.
Newer version available
If a video contains a mistake that cannot be easily recognized by the student, we skip the video. Here's an example.
Sometimes, I won't index a video if I find the explanation a bit too long-winded. Here's an example.
If a video has text that is crucial to what's being taught, yet is too blurry to be read comfortably, then we skip the video. I don't want you to waste your mental energy trying to make out the text. Here's an example where the text is just a bit too blurry. Here's another example where text cannot be read comfortably.
Fails to find an audience
In this video, it's assumed the viewer can fluently multiply but not add. When I'm trying to learn, I find excessive emphasis on old skills to be annoying. I assume, perhaps naively, that others will feel the same.
Distracting animations and sound effects
I won't be indexing these videos. The sound effects, animations, and background are all very distracting.
In this video, the speaker's accent is a bit too heavy, and his English a bit too broken. It takes too much brain power trying to understand what he's saying.
I can't figure out what this guy is saying. Heavy accent, mumbling, slightly broken English, and low audio quality all contribute to me disliking this video.
Requires knowledge outside mathematics
For example, this video asks the odds of picking a vowel from a word ending in Y. The student may know that Y is sometimes a vowel, but may be unsure of when. This is a distraction, and so I won't index videos like this.
Insight is non-mathematical
I will not be indexing problems where the insight is non-mathematical. For example, if the insight is based on the physical constraints of the puzzle, such as this one.
Talking too fast
If you talk so fast it gives me anxiety. Here's an example.
An inch deep and a mile wide
If a video covers lots of topics, but with no depth, the video will be ignored. Here's an example.
I've decided not to index resources which fall under "Displacement, velocity, and acceleration graphs," because I consider this a physics topic much more so than a math topic. That's because you have to know their physical interpretation in order to identify which graph is which, and those are physics concepts, not math concepts.
If a video is overloaded with animations, to the point where it's distracting, we don't index the video. Here's a perfect example.
Here's an example of audio clipping. There are many videos on YouTube like this. I find it ironic that otherwise intelligent people can't figure out how to setup a microphone. If you're microphone is this bad, why even record a video?
If the audio is missing, like in this video.
There is a problem with this video that makes it seem like I have a bad connection. This I find distracting.
Very confusing to follow along with this video because the audio is severely broken.
We don't index robotic sounding voices for the same reason we don't index heavy accents. That is, it takes too much energy to figure out what's being said. Here's a robotic voice that fits this description.
If the camera is all over the place it gives me a headache to watch. I don't want others to stop learning due to a headache, so I don't index videos like this. Here's a perfect example.
This video is skipped because it makes a useless distinction between length and width.
This video fails to find an audience, is poorly edited, and the volume is all over the place.
Too many filler words, such as this video.