Comment Look at a slide-rule for the answer (Score 1) 509
Pick a random spot on a slide-rule. You are more likely to hit a region where the mantissa starts with 1 than any other region.
And as posters have already pointed out, a base-2 slide-rule would guarantee that the first digit is 1.
There is nothing magic about Benford's law, it only shows that random numbers based on measurements are logarithmically distributed.