Todd,
Noonan stated in a letter he could get a Fix +/- 10 miles. Fred being a navigator I presume +/-10 nautical miles, statute miles *1.15.
A navigators rule of thumb says you get lost by 10% over time. If flying 150 mph, add +/-15 miles to the width of your course for each hour flying DR
In the case of the LOP Fred lost the sky during the overcast and got a LOP some time after sun up.
To get the right idea on SkyVector Pick a time between 0618 and 0718 Howland time when the sun would have been at an azimuth of 67 degrees and start with two points +/-10 miles from the center line. Add a quarter mile to the distance from center for each minute you presume Fred is flying DR. If you continue this to Niku the LOP will be almost +/-60 miles. I like to use 0645 and have Fred turn into the LOP at 0745, makes the LOP +/-17.5 miles or about 35 miles wide when he turned into it. You can assign different times from a sunrise LOP to 718 and see the effect of different times. I hope this helps you visualize how flying DR works.
Neff