A little more information on what you are doing would be helpful.

3.6 is reasonably close to 4. Are you sure there isn't an error somewhere in your measurement?

You shouldn't just double values without reason to do so.

Im trying to work out the x value in Na

_{x}WO

_{3} from the unit cell parameter. But to get the unit cell parameter you take d

_{hkl}×sqrt(h

^{2} +etc). I'm also trying to get the miller indicies of (h k l) which obviously requires that the square summed needs to be an integer value.

I've redone the calculations to get 3.6 several times so i'm sure that its not a calculation error. All the other values came out to within 0.05 of an integer so it just seemed like it was out too far to round..