When I developed the Vitamin A Plus, I did a lot of dusting and weighing to come up with a level that I considered to be safe for occasional use.
The best rule of thumb I could give you is that a freshly dusted large adult cricket with Vitamin A plus would contain APPROXIMATELY 200IU Vitamin A (Retinol)
The dose recommended by Mader in his book for Chameleons to treat clinical hypovitamintosis A is 2000IU for every 30 grams of Chameleon Body weight every seven days for two doses.
So using my Vitamin A plus, this would mean 10 large crickets for each 30 grams of lizard.
A little difficult to get a 90 gram chameleon to eat 30 large crickets in a day, but my stuff wasn't meant to be used just for treatment, and more of an overall booster..... or less aggressive and less risky treatment for deficiency than Mader prescribes. It could be just right for specimens that are just showing some signs, but not to the point they need an expensive trip to the Vet.
Allen