Why do I get different precipitation measurements from my TROPO vs. other popular 4” precipitation gauges?

Climaytic says the following:

"This could be due to numerous reasons, but assuming all things equal, the primary reason is because the TROPO gauge is perfectly calibrated whereas other popular 4” rain gauges are not. During our calibration, testing and comparison evaluations, we found that the “Stratus” All-Weather precipitation gauge and the “Outback Blue” precipitation gauge were off by about 4%. In other words, when the Stratus inner tube was filled with 206 g of water, which is mathematically equivalent to 1.00” of water, .04” of water overflowed past the 1.00” marking."