There's no reason for it to change because you're not telling it to change. By default, a graph starts at zero (t0) and increments by 1 (dt). All that you are reading back from the instrument is an array of Y values. If you wire a waveform data type to a graph, it will automatically change the x scale because a wavefrom data type contains t0 and dt information. You can programatically change t0 and dt by creating a waveform data type with the build waveform function. You can also modify the x-scale with a property node. Right click on the graph and select Create Property Node. Right click again and select Change to Write. Right click again and select Properties>X Scale Range. You can select minimum, maximum, increment, etc. You can use the value from the span control to set the range however you need.
