When you start a topic in Fragments and Feedback, and put your 13 lines in the message box, you know you're at exactly 13 lines if you can see all of your 13-line text without scrolling. (If you have blank lines between paragraphs, of course, you'll have to scroll that many more lines to see everything, but only in that case.)
This is also the case if you post any rewritten 13 lines in your topic.
Please be assured that if I cut your "13 lines" it will be according to how the box shows in my browser. This is as fair as I can make it, because I use the same browser and the same box and cut the same for everyone.
Copy and paste the alphabet template below into a reply box on your web browser. If it does not exactly fit the box, then you know your web browser is not showing you a 13-line box, and adapt your "13 line" accordingly.
Alphabet template:
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd
eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
gggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggg
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj
kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk
llllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
1--I do not count the lines between paragraphs when I count the 13 lines, because they should not be there in an actual manuscript.
2--I apply the same grid to everyone in order to be as fair as possible. However, because I'm aware that Firefox puts an extra line in the textarea box, I will allow a 14th line as long as I can see that the author was trying to abide by the 13-line rule (as in self-truncating). I also try to be flexible when considering a line with one very small word in it. If there is other evidence that the author is trying to abide by the 13-line rule, I may not count that tiny-word line.
I'm really trying hard to be consistent and fair, and as far as I can tell (and I check every so often just to be sure), the textarea box that I use in my "judging" has not changed.
I'm very sorry that it frustrates and confuses people at times, but I don't know what else to do to keep things as fair as possible within reason.
I hope this helps, if only a little.