"The E6B "Computer", that's what it was called way back then before Microsoft et al, was basically a circular slide rule with refinements. Among those were scales to convert nautical miles and knots into miles per hour and statute miles. There was also a scale to convert Centigrade to Fahrenheit. The slide rule portion had many uses including calculating distance flown into time elapsed and arriving at ground speed. By factoring in the wind you could calculate your ETA. (Estimated time of arrival).
The reverse of the E6B had a sliding graph that could be used to plot drift. For example if you used the "Double Drift" method you could calculate the wind as follows;
Have the plane turn 45 degrees right and fly this heading for two minutes. (This requires pilot cooperation). Read the drift angle on your driftmeter (another subject) and draw the resultant heading on the isinglass cover of the E6B. Turn 90 degrees left and fly that for two minutes. Draw this heading on the E6B. Turn right 45 degrees, which puts you back on course and take a third reading drawing this on the E6B. You will now have a triangle which will tell you the direction the wind is blowing from and with what force. The great God of Compensating Errors will tell you that this can be used. The isinglass (before plastic) can be erased and used again. Once you have your wind you can recalculate your position and ETA. Don't forget to subtract two minutes from the time run to compensate for the turns off course."
