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# suggestion for:Code Challenge: Creating Flexible Margins

is it really that important to fill in 1.5625% over 1.56% .. feels a litteblit to precise for a quiz , a tip would be to have a solution/hint button to help, so we dont have to guess why the test failed.

is that precision really needed, in web-development ?

@lars -

The key to understanding this, is that when you are converting pixels to percentages, in most cases the fractions of pixels are dropped, not rounded up.

Let's look at the math ...

• `0.0156 * 640 = 9.984`
• `0.015625 * 640 = 10.0`
• `0.016 * 640 = 10.24`

So if you use `1.56%` and drop the fraction, you end up with a 9 instead of 10 pixel margin. However if you use `1.6%` you end up with a 10 pixel margin.

This is due to a combination of how the math works, with how sub-pixel rendering works in most browsers.

aha i see.. thank you so much for the really good explanation, it make sense to me now :D