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I have a base line established in state plane coordinates. I set up at one end backsight the other end and turned an angle to magnetic north. I obtained the declination for the date of observation and added it to the angle to obtain true north. I am approximately 15 degrees different than an observation made years ago. The change in declination over these years would not amount to 15 degrees. What am i not seeing here? If anyone has done this procedure please help.I looked at a USGS quad map and the old angle is close to the angle obtained from measuring on the map.
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