You do not need to use a separate meter. The Wein Zinc Air cell (MRB) is a direct replacement for the original PC625 mercury battery used in all the Canon manual focus SLRs and many cameras by other manufacturers. It has exactly the same voltage, but is expensive. Alternatively The Small Battery Company in the UK offers an adapter that enables cheap hearing aid batteries to be used instead. I use them. I know that there is another company in the US offering a similar adapter.Considering the FTb, TLb and TX, they need mercury batteries to work with them, unless you use a separate lightmeter or the F16 rule.