The DA speeds are based, loosely, on the principle that '10' is the amount of light that results in max black on Ilford MGIV with a #2 filter with a 1 second exposure. '9' is 1 stop less light, '8' is two stops less light and so on.
I am not sure how helpful this data will be, though. It seems you have the version of the Focometer which used a diffusion disk and gave an exposure time for a print with an average ZV (or ZIV or ZVI or whatever you calibrated it to) print tone. They made two models with slider controls and one digital model with push buttons. One of the Leica forums may be able to provide more help.
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