[AndrewC]

Sorry, no. Absolutely no.

O.K. Olympic one. But I just did it.

As you note the Slide rule is actually an adder. It adds lengths. The lengths happen to be measured on a logarithmic scale. The L scale allows you to generate a linear scale. As Vade noted in 1517 with his notched stick(that must hurt) addition is trivial when the stick is so marked. The L scale is linear. Find the first number on the L scale and put the index(left or right) of the slide(C scale) over that number. Next find the second number on the L scale go up to the D scale and read the value. Next using the just found value go to that value on the C scale. Drop down to the L scale and the answer will be there. QED.

There may be some gymnastics involved with the hairline, index, and a left carry. But for 2 number addition you can only carry a one.

[PatrickHenry]

Your technique is difficult to replicate; but I assume you're just consulting the L scale and, in effect, contriving to use the rest of the slide rule as a clumsy caliper for adding L scale lengths. This is not, strictly speaking, "adding" with a slide rule. You could do that crude operation with any measuring stick. It's nothing more than Vade's device. I'm standing by my statement: you can't do addition and subtraction with a slide rule. (And this is so off-topic that I suggest we let it drop.)