The sphere shown in the photographs has an out-of-roundness value (peak to valley on the radius) of 50 nm (2.0×10−6 in). According to ACPO, they improved on that with an out-of-roundness of 35 nm (1.4×10−6 in). On the 93.6 mm (3.69 in) diameter sphere, an out-of-roundness of 35 nm (1.4×10−6 in) (deviation of ±17.5 nm (6.9×10−7 in) from the average) is a fractional roundness (∆r/r) = 3.7×10−7. Scaled to the size of Earth, this is equivalent to a maximum deviation from sea level of only 2.4 m (7 ft 10 in). The roundness of that ACPO sphere is exceeded only by two of the four fused-quartz gyroscope rotors flown on Gravity ProbeB, which were manufactured in the late 1990s and given their final figure at the W.W. Hansen Experimental Physics Lab at Stanford University. Particularly, "Gyro 4" is recorded in the Guinness database of world records (their database, not in their book) as the world's roundest man-made object. According to a published report (221kB PDF, hereArchived 2008-02-27 at the Wayback Machine) and the GP‑B public affairs coordinator at Stanford University, of the four gyroscopes onboard the probe, Gyro4 has a maximum surface undulation from a perfect sphere of 3.4 nm (1.3×10−7 in)±0.4 nm (1.6×10−8 in) on the 38.1 mm (1.50 in) diameter sphere, which is a ∆r/r = 1.8×10−7. Scaled to the size of Earth, this is equivalent to a deviation the size of North America rising slowly up out of the sea (in molecular-layer terraces 11.9 cm (4.7 in) high), reaching a maximum elevation of 1.14 m (3 ft 9 in)±0.13 m (5.1 in) in Nebraska, and then gradually sloping back down to sea level on the other side of the continent.
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The sphere shown in the photographs has an out-of-roundness value (peak to valley on the radius) of 50 nm (2.0×10−6 in). According to ACPO, they improved on that with an out-of-roundness of 35 nm (1.4×10−6 in). On the 93.6 mm (3.69 in) diameter sphere, an out-of-roundness of 35 nm (1.4×10−6 in) (deviation of ±17.5 nm (6.9×10−7 in) from the average) is a fractional roundness (∆r/r) = 3.7×10−7. Scaled to the size of Earth, this is equivalent to a maximum deviation from sea level of only 2.4 m (7 ft 10 in). The roundness of that ACPO sphere is exceeded only by two of the four fused-quartz gyroscope rotors flown on Gravity ProbeB, which were manufactured in the late 1990s and given their final figure at the W.W. Hansen Experimental Physics Lab at Stanford University. Particularly, "Gyro 4" is recorded in the Guinness database of world records (their database, not in their book) as the world's roundest man-made object. According to a published report (221kB PDF, hereArchived 2008-02-27 at the Wayback Machine) and the GP‑B public affairs coordinator at Stanford University, of the four gyroscopes onboard the probe, Gyro4 has a maximum surface undulation from a perfect sphere of 3.4 nm (1.3×10−7 in)±0.4 nm (1.6×10−8 in) on the 38.1 mm (1.50 in) diameter sphere, which is a ∆r/r = 1.8×10−7. Scaled to the size of Earth, this is equivalent to a deviation the size of North America rising slowly up out of the sea (in molecular-layer terraces 11.9 cm (4.7 in) high), reaching a maximum elevation of 1.14 m (3 ft 9 in)±0.13 m (5.1 in) in Nebraska, and then gradually sloping back down to sea level on the other side of the continent.
The sphere shown in the photographs has an out-of-roundness value (peak to valley on the radius) of 50 nm (2.0×10−6 in). According to ACPO, they improved on that with an out-of-roundness of 35 nm (1.4×10−6 in). On the 93.6 mm (3.69 in) diameter sphere, an out-of-roundness of 35 nm (1.4×10−6 in) (deviation of ±17.5 nm (6.9×10−7 in) from the average) is a fractional roundness (∆r/r) = 3.7×10−7. Scaled to the size of Earth, this is equivalent to a maximum deviation from sea level of only 2.4 m (7 ft 10 in). The roundness of that ACPO sphere is exceeded only by two of the four fused-quartz gyroscope rotors flown on Gravity ProbeB, which were manufactured in the late 1990s and given their final figure at the W.W. Hansen Experimental Physics Lab at Stanford University. Particularly, "Gyro 4" is recorded in the Guinness database of world records (their database, not in their book) as the world's roundest man-made object. According to a published report (221kB PDF, hereArchived 2008-02-27 at the Wayback Machine) and the GP‑B public affairs coordinator at Stanford University, of the four gyroscopes onboard the probe, Gyro4 has a maximum surface undulation from a perfect sphere of 3.4 nm (1.3×10−7 in)±0.4 nm (1.6×10−8 in) on the 38.1 mm (1.50 in) diameter sphere, which is a ∆r/r = 1.8×10−7. Scaled to the size of Earth, this is equivalent to a deviation the size of North America rising slowly up out of the sea (in molecular-layer terraces 11.9 cm (4.7 in) high), reaching a maximum elevation of 1.14 m (3 ft 9 in)±0.13 m (5.1 in) in Nebraska, and then gradually sloping back down to sea level on the other side of the continent.
