I've ran into several posts where the author used 2 systems in the same post. Personally, I use the metric/international system all the time. Other people might use other systems, namely the US system. I'm not really comfortable using it myself but I'm fine if others prefer to use it.
The problem arise when the two are mixed in alternation, it's annoying. I think the users can use any system as long as they use it consistently.
What do others think about this?
I agree that this kind of thing is really annoying (though I've probably been guilty of it myself in the past). SI units are the most common ones in science, and given that most of the familiar constants are best known as their SI unit values (e.g. the value of $c$ is ~ 300,000,000 meters/second), I think that they are our best choice.
Either way, consistency in a given post is important. We don't need to have consistency across the board, though - for example, if I reference a table of statistics about population density, I might be working in acres. That could be okay to use across the post, but if there aren't too many numbers, then conversions should be used. Let's not be lazy.
I agree, that one unit of measure should generally be used in a post. I fear I might be one of your culprits though.
