AstroGreg

@Evan It's the derivative from differential calculus - i.e., the "slope" of the function: derivative of sin(x) with respect to x equals cos(x)

@CA I went with Instagram as one of the companies owned by Meta (Facebook) ... so "Meta Data". But I also first tried (unsuccessfully) to figure out how "metadata" worked for the clue.

@Monika Eckhart Yes. It's the average number of earned runs a baseball pitcher would give up in a full game. For 9 inning major league games with 3 outs per inning, it would equal: (# of earned runs given up) / [(# of outs recorded)/27]. So, for example giving up 1 earned run in 3 innings pitched gives: ERA = 1/(9/27) = 3.

@Joshua Cooper Figured it out without the blog, but that was also my only wrong letter ... (also in Ft Collins)