You need to shoot for +- 0.010. Some wheels have offsets, some don't. Its very easy to tell if yours do or not and in the telling you can see how little it matters when you are thinking about truing a wheel. You do not deal with the offset when you true the wheel, that part is done when you lace it. Look at your hub, are the flanges where the spoke holes are located even in height? Now look at your spokes, how many different lengths of spoke do you have? If you have an offset hub you will have at least 3 different lengths or bends of spokes, but if you've only got two different kinds of spokes then there is no offset. Got that? Offset is something that is controlled by the length of the spokes, you deal with it when you lace the wheel. When you are truing the wheel you only concern yourself with the rim's runout laterally and from center. Aside from wheel offset being something that is not addressed when truing its also almost never a high tolerance measurement and even if it was any variance can be addressed with the wheel spacers.
By the way, I also notice that you are giving measurements in fractional inches. Its no problem that you use inches but if you are using fractional measurement then you are clearly not using a dial indicator to true the wheel. You need more accuracy here than a ruler can give you. You need one, a dial indicator that is. You don't just need it for this job either, you'll use it for lots of things. They can be had used for very little money. Thirty to fifty bucks will buy you a high quality dial indicator and various setup hardware in a kit. Its a mighty useful thing to have around
