If your calculator contains ANY kind of java script it will NOT go through the listing process.

What I have been doing is creating shipping calculators for each weight bracket and then loading them on to my Pair webspace. I include a button which links to the appropriate calculator. Above the calculator is a "Back" button so the buyer can go right back to the listing after calculating the shipping. Works just great.

HOWEVER
I have had not been listing for some time and have just started again.
Every item I listed where I put the shipping calculators and entered nothing into the shipping cost box on the screen ended up as FREE shipping and I had to revise each item.

ARGH!!

Besides this problem, items without calculators show up in a search on eBay with shipping costs "Not Specified" - likely a sales killer.
There are items that you just CAN NOT specify flat rate shipping on...you'd lose your shirt or turn people off depending upon your / their location.

We REALLY need eBay shipping calculator function in our listings NOW.