  The analysis of Tables of particle properties shows that the probability
distribution of the results of physical measurements is far from the
conventional Gaussian $\rho(\xi)=exp(-\xi^2/2) $, but is more likely to follow
the simple exponential law $\rho(\xi)=exp(-\xi)$ ($\xi$ is the deviation of the
measured from the true value in units of the presented standard error). A gap
between the expected and actual probabilities grows with $\xi$ very rapidly,
amounting to $ 10^7 $ at $\xi\approx 6 $, and is significant even at $\xi=2 $.
A more detailed study reveals the two-component structure of the distribution:
the $exp(-\xi)$ law is closely fulfilled up to $\xi=3$, but then, at $\xi$
larger than that, the decrease is retarded drastically. This behaviour can be
associated with the existence of two various types of systematic errors, the
detected and undetected ones. Within some model, both types of errors are seen
to affect the form of the distribution, one at moderate $\xi$ and the other at
large $\xi$. The first type (detected) errors are shown in some natural-looking
assumptions to yield the distribution not quite equal but close to the simple
exponential.
