A global electroweak fit combines experimentally measured values of Standard Model physical constants with the theoretical relationships between those constants in the electroweak sector of the Standard Model to determine where, within the range of uncertainties in the experimental measurements the true value of those physical constants is most likely to be. Basically, it uses theory to eke out a bit more precision in our determination of these constants than the measurements make possible in isolation.
The fact that it is possible with experimentally measured value of Standard Model physical constants without serious tensions (which it is) also provides a global test of the consistency of the Standard Model with reality.
The latest paper using up to date experimental data to make a global electroweak fit of Standard Model physical constants can be found here. The discussion of how the input values are chosen (basically, an educated best summary of the data to date) in the paper is also noteworthy.
The global fit of the Z boson mass is 91.1882 ± 0.0019 GeV and the global fit of the Z boson width is 2.4945 ± 0.0006 GeV.
The global fit of the W boson mass is 80.3584 ± 0.0048 GeV and the global fit of the W boson width is 2.090 ± 0.001 GeV.
The Higgs boson mass is 125.13 ± 0.11 GeV. The Standard Model expectation for the Higgs boson width is 4.10 ± 0.06 MeV; a complete global electroweak fit of the data produces 3.78 + 0.30 − 0.27 MeV, which is consistent with the Standard Model expectation. The couplings of the Higgs boson in an electroweak global fit are within roughly 1% ± 1% of the Standard Model expectation.
The global fit of the charm quark pole mass (in the MS scheme) is 1.273 ± 0.003 GeV.
The global fit of the bottom quark pole mass (in the MS scheme) is 4.183 ± 0.004 GeV.
The global fit of the top quark pole mass is 172.67 ± 0.56 GeV.
The global fit of the strong force coupling constant at the Z boson squared energy scale is 0.1179 ± 0.0009.
The global fit of the effective leptonic weak mixing angle is sin^2(theta) = 0.23149 ± 0.00005.
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