What they mean is often the problem. With many of the instruction sets coming out of China, and not matching the parts you got in the box, and if there is a full moon out.......

What most often is the case when they give a number like 3/8" throw, they print a picture or tell you how to use that 3/8". When they don't, the best bet is to consider the measurement to be from neutral to max deflection in one direction. And measure it at the greatest chord location. THEN..........

If you don't have the experience to look at what results and judge the suitability THEN your best bet is to ask an experienced flyer his opinion and see if he will check out the rest of the airplane. And consider seriously having him take it off the first time. He will most certainly be more apt to have encountered models with both too sensitive throws and too insensitive throws. And won't be overwhelmed by how the plane responds.

If you think you can do it, go ahead. That's one way to learn. But before that maiden flight, look at the throws on other models. You'll probably notice that other than 3D models, most don't have over 30degree deflection one way.