Here is my problem. I think I get how to calculate pot odds for ONE card on turn or river but in the charts there are always numbers for turn and river TOGETHER. And THIS I can't find out how to calculate.
Here is how I calculate my odds on the turn:
# of outs divided by the number of unknown cards (47). (this seems to match the charts)
I calculate the river by taking 46 as the number of unknown cards.
Now for a two outer the chart says 8.42 for turn&river together.
I tried to add turn and river odds but that doesn't work out. I tried to divide 4 outs by 47 unknown cards; won't work. Tried the same with 46 - no success. All the time I am close but I would like the EXACT SAME value because I don't think the author of the chart just put random numbers in the decimal places.
Please help me out with this.

Also: When do I use turn&river-together-odds? I was thinking that I should just use odds for the next card and not for the next two. If that matters: I play full ring limit hold'em. I thought that it might be if you need runner-runner but I guess those percentages would be WAY lower.

Please help. I have googled a long time but every site (and there are some) which explains odds of course only tells you how to work out odds for the next card and of course they don't tell you how to work out the turn&river-together odds which they have on their chart.

BTW: I am referring here to percantages :)