Electromagnetic logs LEM are intended to be used on displacement-type and hydrofoil vessels to measure ship's speed through the water and covered distance.
Log LEM 2 is implemented in two modifications: LEM2-1 and LEM2-2.

LEM2-2 has an additional function - measurement of under-keel clearance using a sonar array.
Each log modification has three basic implementations, which differ by the types of bottom-outboard equipment: gate valve inductive transducers, projecting outward the bottom and mounted flush with the ship bottom.

The sonar array is installed in a gate valve.
When the log is installed at the hydrofoil ship, a combined device with inductive and acoustic transducers is used.