How run a Macro if cell A1 equals a value derived from a formula

In the attached spreadsheet Cell A1 contains the formula =IF(E7=50,"X",""). I've recorded a simple macro to write numbers into cells J1:J5 if I press a button. But I want the macro to run when cell A1 shows the letter X. It mustn't run again when X disappears from cell A1. But it must always run when X reappears in cell A1. I can test by manually changing cell E5 to 10, but in "real life" the application will be downloading realtime variable data about oil prices.
Any suggestions greatly appreciated!

You could use something like this in the Sheet1 code module

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