Absence and presence of uncertainties in a data 
In the photo attached, I am comparing the D, Ra, H, and AED values of Glutinous rice in Songkhla (see 4th to the last row) to the rest of the values.  I understand why most of it has uncertainty values (standard deviation).  However, I can't quite understand the implications of some variables not having uncertainty values.
My question is, why do other values don't have uncertainty?  What does this imply when I'm comparing the overall values?

It looks like the uncertainties are reported out to two decimal places. If the uncertainty is so small that rounding to two decimal places gives zero, then I could see why they might choose against writing an uncertainty instead of writing $\pm 0$.
