Your actual data are not accessible and the sub-VI is missing. If you could re-post your VI with time data saved as default on your graph that would be helpful.
In the mean time ... few comments: - You are attempting to display Amplitude vs. Frequency on an XY-graph. However your graph "data" are just two scalars representing respectivelly the single value amplitude and the single value frequency. This will only give you one point on your graph. - What exactly are you trying to display? A set of multiple amplitudes vs.frequencies? The spectrum of your signal?
