(modx 1.0.2)
By default the ditto.2 iteration starts at 0,

to have it start at 1 use
[+ditto_iteration:math=`?+1`+]

assuming you have PHx installed this should work,
also use "ditto_iteration" not "iteration", this little ooopsies cost me a bit of time

Just started using PHx in modx, and I'm pretty excited about it...