When the chart plotter failed during the Harvest Moon Race we used my i-pad to find the Buckner mark as well as 5A & Green 11 to finish the race. Problem was, we had to keep it off most of the time to conserve the battery life. This past Saturday I used it to plot a four lap race and lieu if setting marks. Each lap had four marks and each lap was 7.7 miles. The tracks indicated that we never rounded the marks at the same location when in-fact we did during the actual rounding, according to the Navionics chart. We did have the i-pad plugged into a support battery. I lost some confidence in the accuracy of the Navionics program based on the tracks relationship to the marks after we finished the four laps. We set the marks using the lat/long coordinates.