A co-axial time-of-flight mass spectrometer having a longitudinal axis and first and second ion mirrors at opposite ends of the longitudinal axis. The lockable differential generally comprises an actuator and a locking mechanism. Data is retrieved for the prefetch thread and stored in a memory, such as data fetched from an external memory and stored in a buffer. Another aspect of the invention includes altering the flow of gas to different regions of the plasma in response to differences in the integrated power spectra detected by the fiber optic sensors. , flags are raised for the neighboring pixel and a neighboring pixel which are symmetrical.