Dynamic effects and lateral fluxes are possible error sources.
Some of the uncertainties in the input parameters cannot be improved and will remain as error sources.
The weather is perhaps the biggest error source.
However, there are many other external error sources other than the disk itself.
That is really not a good teaching tool, because the number of confounding variables and error sources many.
The processing of available data does not compensate for the error sources without the traditional concepts:
This is a generally result of simple operational models to compensate for the plurality of error sources.
The second error source enfolded in the decomposition is more subtle and requires a little bit of calculation.
A more comprehensive outline of these error sources is given in Meng et al.
Buffle et al. (1972) discuss a number of error sources.