Yeah,, I believe most of those big numbers (more than 10 significant digits ) are result of inverted direction of the conversion units.. Miles to Kilometers is the perfect example of that..

Miles to Kilometers, you multiply by 1.609344 ( only 7 significant digits required)

but the reverse direction, if you want to use the multiply factor.
Kilometer to Miles, you have to multiply by ( 1 / 1.609344 ) = 0.62137119223733..... , a lot more significant digits this way.