The features you see in a signal when you use an oscilloscope to look at a signal are features you cannot see otherwise.  In this lesson you will learn about oscilloscopes and you should keep this goal in mind as you proceed through the lesson. An oscilloscope is easily the most useful instrument available for testing circuits because it allows you to see the signals at different points in the circuit. The best way of investigating an electronic system is to monitor signals at the input and output of each system block, checking that each block is operating as expected and is correctly linked to the next. With a little practice, you will be able to find and correct faults quickly and accurately,

      Faced with an instrument like this, students typically respond either by twiddling every knob and pressing every button in sight, or by adopting a glazed expression. Neither approach is specially helpful. Following the systematic description below will give you a clear idea of what an oscilloscope is and what it can do.

The function of an oscilloscope is extremely simple: it draws a V/t graph, a graph of voltage against time, voltage on the vertical or Y-axis, and time on the horizontal or X-axis.As you can see, the screen of this oscilloscope has 8 squares or divisions on the vertical axis, and 10 squares or divsions on the horizontal axis. Usually, these squares are 1 cm in each direction:

When a sinusoidal signal is applied, then the vertical clamp meter position is proportional to the voltage at any instant.  If you applied a low frequency sine signal, you would get a track like the one below.  If you have a sinusoidal signal that repeats every half millisecond - a frequency of 2kHz - you would get a picture like this one.  It would appear to be stationary on the oscilloscope screen, but it really isnt.  Its just that it repeats so frequently that you see it as a constant image.The Oscilloscope has evolved from the basic Analog Oscilloscope to the Digital Storage Oscilloscope (DSO), and now the latest, the Digital Phosphor Oscilloscope (DPO), which is the best of both the Analog scope and the DSO,Some scopes have such a wide bandwidth, that no passive probe is able to do it justice, and the only way to use the maximum bandwidth of this type of scope is to drive the scope from a 50 ohm source through a 50 ohm coax, terminated into 50 ohms at the scopes input. In fact, some high performance scopes have a 1Meg ohm/50 ohm termination switch for just such occasions.