How to pass in a ratio of 4/15 (instead of its approximated decimal form of 0.266) to table definition.
Final solution can be seen here.
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If you want more accurate calculations use the fp package.
For example using the fp package as shown below you get
No need for any manual calculations!
You can use it in a tabular as follows (remember it creates variable names on the fly)
I cannot see a gap with a zoom of 400% ...