Well the gyro reading depends on the sensitivity you have set for the device.
At the most sensitive setting, the gyro reading represents 131 LSB per degree of rotation, per second.
Where LSB refers to the least significant bits of the 12 or 16 bit binary number representing the
So ( on that setting of the device ), an increase of 1 in the binary number represents an increase
of (1/131) of a degree per second in the measured rotation rate.
An increase of 131 in the binary number represents an increase of 1 degree per second in the measured
Those readings you have there of about +250 in the z axis means there is a rotation of about 2 degrees per
second of rotation about the Z axis. ( because 250 is roughtly twice 131 ).
If this was really happening, the device would turn right around in about 3 minutes, because it takes 180
seconds to turn full circle at 2 degrees per second.
You can set one of the other gyro sensitivity levels, you get less sensistive readings that way but you get
to be able to read really large rotations.