Full scan is useful in determining unknown compounds in a sample. It provides more information than SIM when it comes to confirming or resolving compounds in a sample. Most instruments are controlled by a computer which operates a computer program called an "instrument method." The instrument method controls the temperature in the GC, the MS scan rate and the range of fragment sizes being detected. When a chemist is developing an instrument method, the chemist sends test solutions through the GS-MS in full scan mode. This checks the GC retention time and the mass fragment fingerprint before moving to a SIM instrument method. Specialized GC-MS instruments, such as explosive detectors, have an instrument method pre-loaded at the factory.