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