Problem understanding impedance measurement device accuracy format
"rdg" means reading and "dgt" means digit. This specification means that there are two defined types of error.

First, there is an error of up to \$\pm 0.4\$% of the meter reading. Multiply the displayed value by 0.004 to find the actual value of this error. For the displayed value of \$1.1424 \mathrm{m}\Omega\$ the error is about \$\pm 4.57\mu\Omega\$.

Second, there is an error of \$\pm8\$ in the least significant digit of the display. For the example you provide, the place value of the least significant digit in the display is \$0.1\mu\Omega\$ so there is an additional error contribution of \$\pm 0.8\mu\Omega\$.

So you have a total error specification of \$\pm 5.37\mu\Omega\$ for this measurement. The errors in digital meters are typically specified in this way, as a percentage of the reading and as a fixed multiple of the least significant digit.