1
The second error is systematic, the third is an estimate of theoretical uncertainties.
References:
KOTULLA
2002
PRL 89 272001
The Reaction ${{\mathit \gamma}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \gamma}^{\,'}}{{\mathit p}}$ and the Magnetic Dipole Moment of the ${{\mathit \Delta}{(1232)}^{+}}$ Resonance