3 spaces seemed to be the norm for block-structured languages (Pascal, PL/I, Cybil, PLUS, etc.) back in the "card image" days before tabs appeared in C source f

3 spaces seemed to be the norm for block-structured languages (Pascal, PL/I, Cybil, PLUS, etc.) back in the "card image" days before tabs appeared in C source files. I think it worked because chains of END would line up in a nice diagonal. I got used to 2 spaces in C++ in a big shop overrun with Style Guide fundamentalists and really long API names, but it's just not enough to convey logical nesting at a distance. I've seen code, can't remember where, that used 4 space indentation for loops and 2 spaces for conditionals, so that indentation depth more accurately reflected runtime cost.