I have a couple of DX-60s to "get to" sometime in the future. Meanwhile I'm collecting info on these rigs. One is a DX-60 and one is a DX-60A. I have a manual for the DX-60 but not for the DX-60A. What are the differences (aside from a different meter) between the DX-60, the DX-60A and the DX-60B?