In the example Measure Jitter the jitter is independent of the bit rate as well. The jitter is added as a fraction of the bit period and the other added noise is quite low. The fact that the H. Range value changes for large sample rates is because the increased number of samples will increase the chance of data points far outside the normal deviation. This is why a simple range is not often used in statistics. If you compare the H. Std. Dev. they are much more similar for different sample rates.
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