That depends on what scope you have and what interface options the scope has.
The instrument will typically have a GPIB interface. With a GPIB card in your PC you can send commands to the scope and receive data and status back.
To see an example of GPIB communication, see the gpibrw sample project that ships with CVI at ..\CVI\samples\gpib\gpibrw.prj. You can use this example as is with a scope hooked up to your PC with gpib.
You'll need to know what GPIB address your scope is set to. On a newer Tek scope, goto Utilities >> GPIB Configuration to see or set the GPIB address.
A sample programming manual is available from the Tek website at http://www.tek.com/Measurement/Solutions/openchoice/docs/scope_manuals/PHP0197V4.pdf
In this manual, you can find details o
n the HORizontal[:MAIn]:SCAle command.
