For BU analysis in semi-log plot, there are two well known time-functions, Horner time and Superposition time. Horner time is used for a BuildUp after a single constant rate history and Superposition time is used for multi-rate history.
Ecrin, by default plots semi-log with Superposition time function. I was trying to plot a semi-log for BU for an exercise. I am able to plot Horner time by (tp+delt t)/del t (where terms have their usual meaning). It gives me a plot where for every pressure point I'm able to calculate a Horner's Time.
For Superposition time,

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I'm not able to understand that how can I get a superposition time for every pressure point in the BuildUp to plot a semi-log.