The External Attenuation, in the Vertical menu, allows the user to compensate the oscilloscope for attenuation that is applied outside the oscilloscope, such as power dividers, inline attenuators. For example, a power divider splits an incoming signal in half. If the user wishes the oscilloscope to properly show the signal amplitude before the power divider, the External Attenuation would be set to 2 (linear). This will increase the Volt/Div setting by 2. All measurements and cursor reading will reflect this change the vertical scaling. This will save the user from having to factor in any attenuation manually. Note: External Attenuation DOES NOT change the attenuation within the oscilloscope. The External Attenuation function only modifies the vertical scaling to account for external attenuations the end user is using.