How to Decode a British Standard Mortice Lock with GJ locks Decoder 

Mortice lock decoding is a technique we use here at Liberty Locksmiths libertylocksmi....
The tool is a GJ locks Era fortress decoder which also decodes Union strongbolt and new style Yale British standard mortice locks.
It works by reading the lever heights. There are 5 levers.
When your reader wire is on the lever you use a chart to read the lever height. Once you have the five numbers corresponding to the levers inside the lock you can make a temporary key and open the lock. The aim is to get into a mortice lock without damaging it if someone lost their key. They can also be picked but this way causes less stress in the lock.