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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@DrAzzy
My interpretation is that their thinking was "Oh, we'll leave out the crystal so the person developing with this can run it at whatever speed they want" - but this means you need a crystal to make it run at 84 x_x
I think it's the black one, X2, that's used to set the clock speed of the MCU, but I'm not certain.