This Longines looks close to unused and I doubt it’s ever been opened before. This is a late 70’s diving chronograph with a depth meter built in the crystal. This works where there is a red marker inside a tube in the crystal, the opening of this tube is blocked by the water, and the air inside is trapped. When you dive deeper the air in the tube compresses and the water comes in pushing the red marker indicating the depth on the bezel. This is not developed by Longines, but they bought the right to have some made branded as Longines. As it’s never had a service it could probably do with a service.