For example, consider a process where a known mass of A enters a system, and after the process occurs, masses B and C exit. We can measure the mass of B but not the mass of C. Since mass is conserved, the mass of C is equal to the mass of A minus the mass of B. After repeating the experiment and measurement

*n*times, we could have an estimate of the mass of C that looks like 0.2 kg (95% CI, -0.2 - 0.7).

Here is where my question comes into play: since we cannot have a negative mass of C, is there a valid method for "truncating" the lower bound of the uncertainty?

I considered just changing the lower bound and writing 0.2 kg (95% CI, 0 - 0.7), but this opens up more questions. First, is this now a 97.5% CI, since the left tail the uncertainty is cut off, should I have started with a 90% CI to get to 95% after this method? Moreover, this method produces strange results for more extreme examples: if the mass of C started out as -0.2 kg (95% CI, -0.5 - -0.1), do we correct this to 0 kg (95% CI, 0-0)?

I am wondering if there is a standard math based method to perform this adjustment.