Choosing the best automatic tank gauge for your application largely depends on the number of tanks that you need to monitor. The Veeder Root TLS-4c is capable of monitoring 2 tanks and TLS-4i is capable of monitoring 4 tanks. This limitation is based on the number of sensor inputs available to each tank. At a minimum, each tank requires a level probe, sump sensor and interstitial space monitor. The Veeder Root 450PLUS is capable of monitoring up to 64 tanks and can track 99 sensors of any one type.