# DI (δ-δ)

DI (δ-δ), Deterministic Interference, is a measure of the amount of vertical interference on a signal due to deterministic causes.

DI is measured using the following steps:

1. The instrument measures Random Noise (RN), Periodic Interference (PI), and Inter-Symbol Interference (ISI).
2. The ISI histogram for the one level is convolved with the histogram of the one level RN and PI data, and the same is done for the zero level data. These histograms are referred to as the Total Interference (TI) histograms.
3. Using the measured value of RN, a dual-Dirac model is fit to the TI histogram. The model is fit at a probability of 10E-3 divided by the pattern length.