Perspective #1. The chart below tabulates the AFFTA line standards. There are no half line weights in that standard. The difference between a 3 weight line and a 4 weight line is 20 grains (a.k.a., 0.05 ounces or 1.3 g). That difference is equivalent to 6 feet of a 3 weight fly line. Less than a rod length.
Nobody has reported any line weight measurements (hint:
it is easy to do). However, terms such as 'true', 'light', 'heavy', and 'half weight' have been used prolifically in this thread. These are just opinions when they lack empirical data to back them up. Please treat them as such.
Perspective #2. There is no such thing as a 3 weight rod. Sorry. Go to the
affta.org/page/IndustryStandards website. Have a look around. There are standards for fly lines, spey lines, and reel feet. There is no standard or suggested method for rating rods. So where does that number on the side of the rod come from? The number is the opinion of the rod maker. Unlike fly lines, there is no way to back up a rod rating with measurements.
Many of us frequent this forum because our opinions vary from the mainstream of fly fishing. Within the forum, our casting styles vary, our age and muscles vary, and our available equipment varies. In particular, our favorite waters vary. Our opinions should vary too. Please understand that when you post. Cut your fellow forum members some slack.
Tom