Night diving for lobsters is the best time to do it because the lobsters walk around at night looking for food. During the day they tend to hide in the shadows of rock or coral holes out of sight. The advantage is yours, but you either need to work as a buddy team to preform all the steps of bagging legal bugs (lobster) or grow a third arm. Holding a dive light, measuring the catch takes two hands, a third one is required to bag the bug! Attaching a gauge to the front of your dive light can make the job easier. Make sure all your lobster catches are keepers! This corrosion-resistant lobster caliper gauge is the legal type required by most Fish and Game Departments. Measuring in most cases is accomplished by measuring from between the lobster's eye sockets to the end of the carapace (Body). The Trident Light Mounted Lobster Gauge fits lights 2 .75" to 5" (7cm to 12.7cm) in diameter. Includes aluminum 3 1/4"(California regulation)and 3" (Florida regulation)lobster measuring gauge with stainless steel attachment for most night diving lights.