The TPU is a rack mount that is about 4 years old but has only one hour on it to test. The 600 kHz fish is 10 years old but new transducers were put in about 4 years ago and it and the 900 kHz fish have only a test hour. Shortly after the TPU was factory replaced, the 600kHz fish was manufacturer refurbished and the purchased new 900 kHz fish has never been in the water. Had to upgrade to a dual frequency CHIRP system to satisfy government contractors. That is the reason we have not used the advertised Marine Sonic since manufacturer refurbished the system. Originally, this Marine Sonic system sold for $25,000. The new TPU, 900 kHz fish and refurbishing the 600 kHz fish cost $12,000