DC nullifier for oscilloscope input:

Inspecting and analyzing low-frequency signals superimposed on a fairly high-level direct voltage with an oscilloscope, set to its a.c. position, is not as straightforward as you might wish as anybody who has ever tried it will testify. One satisfactory way of performing such tests is by removing the direct voltage from the input signal to the oscilloscope. The adapter described in this article was designed to do just that.