i bought an OTC 1340f labscope, and i bought an amp clamp for it aswell.

i was wondering if anybody with labscope experience could tell me i just bought the OTC1340F labscope and then i bought an ampclamp for it aswell, this scope has a BNC connection for the leads, now if i have the amp clamp attached to the BNC, connection on the scope do i still need to run a ground lead to a common ground? or is it internally grounded in the scope itself/ im having trouble getting a good waveform, if anybody is familiar with labscopes plz help thanx....