The software does not allow calculations, but one can use a piped link to a calculation with Google's calculator, with the label as answer, to demonstrate the numbers used in the computation. This way one can check for consistency, see the result with a higher accuracy, and also conveniently update the result.
E.g., in the case of the population density in the Netherlands:
[[google:16318199/33883|482/km²]], giving 482/km².
With a suitable browser the evaluated expression pops up, so the link is useful even without following it.
Suppose that someone updates the population figure but not the density, than the next person can see that the density is not based on the latest figure, replace the first number, press Preview, follow the link, copy the new result to the link label, and save. Thus the update requires a minimum of effort.
Unfortunately, the result 482 has to be entered manually and consistency is not automatically maintained.
Without putting the result on the page 
Alternatively, the user has to follow the link to see the result. Using Template:Popd is convenient and there is no redundancy, hence no worry about consistency:
- Population: 16318199
- Area: 33883 km²
- Population density (people/km²)