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3D3DGyroscope sphere.
These spheres appear from time to time on eBay and tend to go for pretty high prices. They are said to be from an air force gyroscope: The sphere would be spinning at very high speed, suspended electrostatically. The markings on the surface allowed the system to track the orientation of the sphere as it was spinning. It's commonly claimed that they are extremely accurate spheres, within millionths of an inch of perfect. Or at least, they were until they inevitably crashed into the wall, got scratched or bent, and thus ended up on eBay. Here's what the seller had to say about this particular one:
This is a hollow beryllium Electrostatically Suspended Gyroscope (ESG) Sphere used in the Inertial Guidance System of the B52 and F117 bomber Aircraft.

This high tech unit was designed to rotate over 50,000 times a minute and electrostatically suspended in a near perfect vacuum.

While in flight use aboard the aircraft it had a catastrophic failure and crashed in its housing. This caused a distortion of this near geometrically perfect oblate sphere.

Note: This particular sphere has only minor scratches (less than one thousandth of an inch deep) and is in otherwise good condition.

It originally measured 1.50000 inches in diameter, weighs 10 grams and has a highly polished optical surface. There are a series of etched patterns used to read out the position and speed of this sphere with a set of photovoltaic sensors.

The guidance system it belonged to was known as the Standard Precision Navigator/Gimbaled Electrostatically Suspended Aircraft Navigator or SPN/Geans. The SPN/Geans was the prime inertial position and velocity sensing system for the aircraft.

This gyroscope originally cost the government over $17,000 and was so expensive to maintain that it was discontinued from service.
This is very similar to what other sellers say about similar spheres, and having to reason to doubt it, I think it's probably all true. See the next sample for a fascinating variation on the theme: A broken gyroscope sphere.
Source: eBay seller spatial-one
Contributor: Theodore Gray
Acquired: 29 February, 2004
Price: $98
Size: 1.50000"
Purity: 99%