The reign of antenna gain pain

Do you know the difference between dBi and dBd? Do you know how antenna directivity and gain relates to each other?

Here is a nice website:

http://www.hamradio.me/tech-talk/antenna-gain

For some reason, some antenna manufacturers, even some big corporate outfits, get away with constantly lying about the gain of their products.

http://www.hamradio.me/antennas/g2bcx-slimjim-gainflation.html