Wierd format output

[ethan+@pitt.edu]

This may seem silly, but I can't understand:

? (format t "~%~10,1,1E" 15)
    1.5E+1
? (format t "~%~10,1,1E" 15E12)
   1.5E+13
? (format t "~%~10,1,2E" 15)
   2.0E+01

Why is there a rounding error in the last example?  Why is there
rounding at all?

Thanks,

Ethan

Ethan Benatan
ethan+@pitt.edu