I've seen the MR Dial, Arredondo Accessories powder bar and a couple of other powder bar adjuster enhancements, but the best one I've seen is an actual micrometer head that replaces the original powder bar adjuster bolt. I found it at www.uniquetek.com.
Anyway, since it is a micrometer, it allows you to return exactly to any powder weight that you have used ... if you remembered to write down the micrometer setting. I installed one on my XL650 and it works great.
LeeL