It's the diameter and where would I find that stamp?

Thanks for confirming the dimensions.
The stamp is usually in very small letters on either the top or bottom rim (probably not both).

I can't seem to see a name on those locations. I reason I wanted to get it appriased was because I found the receipt from 1982 and thought 700 dollars was a lot for a chandelier

I would be VERY surprised if this was marked - the workmanship doesn't look sufficiently superior to attribute this to their shop. A retail price of $700 in 1982 would have been on the high side (but not unreasonable) for a quality reproduction shade. I'll evaluate this as a Tiffany style dragonfly chandelier shade with the caveat that a first-hand examination may be warranted to confirm the value.
Based on the photos and information provided, and subject to examination, this is:

An Art Nouveau art glass "dragonfly" chandelier lampshade
Tiffany style, early 20th Century
The conical shade with large inverted dragonflies against a yellow ground; apparently unmarked
approximately 25 inches diameter
PROVENANCE: acquired in 1982 for $700.
$1,000-1,500*
*represents a fair-market value for auction purposes; retail or asking price may vary.

Please let us know if you have additional items to appraise, and thank you again for using Mearto.