Locking in vnmr
From NMR Wiki
In the vnmr command line type 'acqi' or click 'Acqi' button. A window as shown on Fig. 1 will open. Now click "Lock" button. The window will change into something like you can see on Fig. 2 or 3.
The curve that you see in the window is an FID (free induction decay) of lock nucleus (most often-deuterium).