A standard deviation is required when calculating peak-to-peak jitter. Since true peak-to-peak jitter is random and unbounded, it is important to always associate a bit error ratio (BER) when specifying a peak-to-peak jitter limit. Without it, the specification does not have a boundary and will continue get larger with sample size. Given that a BER is application specific, many frequency timing devices specify jitter as an RMS. This allows the peak-to-peak jitter to be calculated for the specific application and BER requirement. Because a standard deviation is the variation from the mean of the data set, it is important to always calculate the peak-to-peak jitter using the typical RMS value. The table below shows the BER with its appropriate RMS Multiplier. There are two columns for the RMS multiplier: one should be used if the signal is data; the other should be used if the signal is a repetitive clock signal. The difference between the two is the data transition density (DTD). The DTD is the number of rising or falling transitions divided by the total number of bits. For a clock signal, they are equal, hence the DTD is 1. For Data, on average, most common encoding standards have a 0.5 DTD. Refer to application note AN-838 for more details. For other questions not addressed by the Knowledge Base, please submit a technical support request.