If you multiply each of these by 1000, so that the decimal point disappears, you can easily see which is bigger:

6430 and 6359. It's clear that the first number is bigger than the second.

When you multiply by 1000, you just move the decimal point 3 places to the right (each zero moves the number one place to the right). If you run out of places to move, just insert a zero. 1000×6.43=6430 because there were only 2 decimal places, so you need an extra zero to make up for the missing decimal place. Another example, 1000×6.3=6300 because you need to make up for 2 missing decimal places.