Plots with the 3m15s rule are not (in theory) affected by your own movement. If you are stationary then all bearings are plotted from the same place. If you are moving the bearing lines are started all equally displaced point. (and here is where the theory disclaimer comes in) The endpoints, where the target are are also equally displaced according to the target's motion.
But, if you dilly-dally and take your time between range measurements and plotting them on the map then the plot lines are not started from where the range and bearing was measured initially. That's no problem if ALL plot lines are late/displaced equally. In other words late by the same amount of seconds. But if you are quick with one plot, and very late with another then you won't get an accurate target track. The trick is to be consistant. Or average over enough plots.
You can safely make course and speed changes all you want when plotting, aslong as those lines are started from where your uboat was when the rangemeasurement was done. Just don't get sighted in the process.
Your speed and course wil affect the outcome of the speedmeasurement from the notepad-procedure. But that's not plotting, or the 3m15s rule.
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