You're looking at a hexadecimal representation of a floating-point number. If you're new to those, you can use an
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to experiment with different values. The byte order is flipped, but you can click the "Swap to use big-endian" checkbox to make things simpler. Your screenshot shows the hex bytes for float value 1.9375.
If you're just looking for basic customization, please
use the in-game slider first. You'll find it on the Settings menu (available on the title screen; also available in-game by pressing Esc). It will let you fine-tune a value somewhere between 0 and 2 (note: the middle/default value of the slider is 1.0).
The only reason to do registry-editing is if you're determined to go
beyond the normal bounds. Please note that extremely high values will generate silly outcomes (e.g. minutes-long ejaculation).