reference will now be made to the drawings to describe the exemplary embodiment of the device and the method , in detail . referring to fig1 , a device 10 for measuring an eccentricity of an optical disk 20 in accordance with an exemplary embodiment is illustrated . the device 10 includes a spindle motor 30 , an optical pickup 40 , a focusing servo circuit 50 , a tracking servo circuit 60 , a system control circuit 70 , and a signal processing circuit 80 . the spindle motor 30 is configured for supporting the optical disk 20 thereon and driving the optical disk 20 to rotate at a predetermined rotational speed . the optical pickup 40 is electronically connected to and controlled by the focusing servo circuit 50 and the tracking servo circuit 60 . the optical pickup 40 includes a detector 42 , a light source ( not shown ), and a plurality of optical lenses ( not shown ) therein . the light source is capable of emitting a light beam 44 . the optical lenses are capable of focusing the light beam 44 on the optical disk 20 . the detector 42 may be a photo diode and configured for detecting the light beam 44 reflected from the optical disk 20 and outputting electronic signals based on the received light beam 44 . the focusing servo circuit 50 includes a focusing error signal generator 52 , a focusing compensation circuit 54 , a switch 56 , and a focusing drive circuit 58 . the focusing error signal generator 52 is electronically connected to the detector 42 for receiving the electronic signals and generating focusing error signals . the focusing compensation circuit 54 is electronically connected to the focusing error signal generator 52 for receiving the focusing error signals and outputting focusing compensation signals based on the focusing error signals . the focusing drive circuit 58 is electronically connected to the focusing compensation circuit 54 via the switch 56 . the switch 56 is turned on / off in accordance with signals outputted from the system control circuit 70 . if the switch 56 is turned on , the focusing drive circuit 58 is capable of receiving the focusing compensation signals from the focusing compensation circuit 54 and sending out focusing drive signals to adjust / move / drive the optical pickup 40 , that is , a focusing servo operation for moving the light beam 44 along a direction y perpendicular to the optical disk 20 is performed . if the switch 56 is turned off , the focusing compensation signals from the focusing compensation circuit 54 cannot be fed to the optical pickup 40 thus , the focusing servo operation is not performable . the tracking servo circuit 60 includes a tracking error signal generator 62 , a tracking compensation circuit 64 , a switch 66 and a focusing drive circuit 68 . the tracking error signal generator 62 is electronically connected to the detector 42 for receiving the electronic signals and generating tracking error signals . the tracking compensation circuit 64 is electronically connected to the tracking error signal generator 62 for receiving the tracking error signals and outputting tracking compensation signals . the tracking drive circuit 68 is electronically connected to the tracking compensation circuit 64 via the switch 66 . the switch 66 is turned on / off in accordance with signals output from the system control circuit 70 . if the switch 66 is turned on , the tracking drive circuit 68 is capable of receiving the tracking compensation signals and sending out tracking drive signals to adjust / move / drive the optical pickup 40 , that is , a tracking servo operation for moving the light beam 44 along a direction x parallel to the optical disk 20 is performed . if the switch 66 is turned off , the signals from the tracking compensation circuit 64 cannot be applied to the optical pickup 40 so that the tracking servo operation is inactive . the signal processing circuit 80 includes a shaping circuit 82 , a first counter 84 , a second counter 86 , and an operation circuit 88 . the shaping circuit 82 is electronically connected to the tracking error signal generator 62 for receiving the tracking error signals in a sinusoidal waveform and transforming the tracking error signals in the sinusoidal waveform to a rectangle waveform . the first counter 84 is electronically connected to the shaping circuit 82 , and configured for counting a tracking error signal pulse count . the second counter 86 is electronically connected to the spindle motor 30 for receiving and counting an electronic signals pulse count of the electronic signals sent by the spindle motor 30 . a quantity of tracks traversed by the light beam 44 is determinable by the first counter 84 , and a number of revolutions that the spindle motor 30 rotates is determinable by the second counter 86 . the operation circuit 88 is electronically connected to the counter 84 for calculating an eccentricity of the optical disk 20 based on the quantity of tracks traversed and the number of revolutions ( e . g ., the quantity of tracks traversed per revolution ) and outputting a result signal to the system control circuit 70 . the memory 90 is electronically connected to the operation circuit 88 and configured for storing a reference value . the eccentricity of the optical disk 20 can be compared with the reference value . the reference value can be changed in accordance with different precision requirements . referring also to fig2 , the device 10 can be operated as follows . first , in step s 10 , the optical disk 20 is placed onto the spindle motor 30 . second , in step s 12 , the optical disk 20 is rotated at a predetermined rotational speed by the spindle motor 30 . third , in step s 14 , the system control circuit 70 signals the switch 56 to turn on and signals the switch 66 to turn off ; thus , the focusing servo operation is activated and the tracking servo operation is inactivated . fourth , in step s 16 , the detector 42 detects the light beam 44 reflected from the optical disk 20 , and outputs electronic signals transformed from light signals in the reflected light beam 44 . the focusing error signal generator 52 receives the electronic signals from the detector 42 and outputs focusing error signals to the focusing compensation circuit 54 . the focusing compensation circuit 54 outputs the tracking compensation signals to the focusing drive circuit 58 via the switch 56 . the focusing drive circuit 58 adjusts the optical pickup 40 . the light beam 44 emitted from the optical pickup 40 is thus projected on the optical disk 20 . fifth , in step s 18 , the tracking error signal generator 62 processes the electronic signals from the detector 42 and outputs the tracking error signals in the sinusoidal waveform to the shaping circuit 82 . sixth , in step s 20 , the shaping circuit 82 transforms the tracking error signals in the sinusoidal waveform to the rectangle waveform and outputs the tracking error signals in the rectangle waveform to the counter 84 . seventh , in step s 22 , the first counter 84 counts the tracking error signals pulse count to determine the quantity of tracks traversed by the light beam 44 , and outputs signals to the operation circuit 88 . eighth , in step s 24 , the second counter 86 counts the electronic signals pulses count of the electronic signals from the spindle motor 30 to determine the quantity of revolutions the optical disk 20 rotates , and outputs signals to the operation circuit 88 . ninth , in step s 26 , the operation circuit 88 calculates the eccentricity of the optical disk 20 based on the quantities of the tracks and the revolutions . the eccentricity of the optical disk 20 can be easily calculated . for example , the eccentricity approximately equals to the number of the tracks traversed by the light beam 44 in one revolution divided by a constant . the eccentricity can be also described by deviating distance of the tracks relative to a center of the optical disk 20 and can be easily calculated because widths of the adjacent tracks and track pitches are known from published specifications of the optical disk 20 , and the number of the tracks traversed by the light beam 999 on the optical disk 20 in one revolution can be counted . tenth , in step s 28 , the operation circuit 88 compares the eccentricity of the optical disk 20 with a reference value stored in the memory 90 to analyze the eccentricity of the optical disk 20 . if the eccentricity of the optical disk 20 is greater than the reference value , the optical disk 20 is identified as an eccentric disk ( step 30 ), and the system control circuit 70 outputs a signal to turn on the switch 66 ( step s 32 ). the tracking drive circuit 68 can thus receive the tracking error correction signal and output electronic signals to adjust the optical pickup 40 to moving the light beam 999 to a correct track . if the eccentricity of the optical disk 20 is less than the reference value , the disk 20 is identified as a regular disk ( step s 30 ). the eccentricity of the optical disk 20 can thus be simply measured and adverse effects due to the eccentricity can be greatly reduced . the embodiments described herein are merely illustrative of the principles of the present invention . other arrangements and advantages may be devised by those skilled in the art without departing from the spirit and scope of the present invention . accordingly , the present invention should be deemed not to be limited to the above detailed description , but rather by the spirit and scope of the claims that follow , and their equivalents .