A measurement of Newton's gravitational constant
G
has been made with a cryogenic torsion pendulum operating below 4 K in a dynamic mode in which
G
is determined from the change in torsional period when a field source mass is moved between two orientations. The source mass was a pair of copper rings that produced an extremely uniform gravitational field gradient, whereas the pendulum was a thin fused silica plate, a combination that minimized the measurement's sensitivity to error in pendulum placement. The measurement was made using an as-drawn CuBe torsion fibre, a heat-treated CuBe fibre, and an as-drawn Al5056 fibre. The pendulum operated with a set of different large torsional amplitudes. The three fibres yielded high
Q
-values: 82 000, 120 000 and 164 000, minimizing experimental bias from fibre anelasticity.
G
-values found with the three fibres are, respectively: {6.67435(10),6.67408(15),6.67455(13)}×10
−11
m
3
kg
−1
s
−2
, with corresponding uncertainties 14, 22 and 20 ppm. Relative to the CODATA2010
G
-value, these are higher by 77, 37 and 107 ppm, respectively. The unweighted average of the three
G
-values, with the unweighted average of their uncertainties, is 6.67433(13)×10
−11
m
3
kg
−1
s
−2
(19 ppm).
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