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In case anyone else was wondering, if you want a reference to a cell in Google Sheets to not change when you copy and past it elsewhere, you want an "absolute reference." To make a reference absolute, you have to put a $ before both the row and column. e.g. If you want a formula to always refer to cell C19 no matter where it's copied and pasted, you'd refer to it as $C$19.
A lot of the top search results for this were trying to get me to watch a video. Never, motherfucker! Never!