I still have one of those somewhere. It is probably about 70 years old. It load tests each cell individually back when the straps between cells were exposed. During the 1970's the straps between cells were no longer exposed. Probably in the mid 1970's I purchased a carbon pile load tester put the entire battery under load to test. Several years ago I purchased a very expensive battery diagnostic system. I am disappointed in the tester. I still prefer to use the carbon pile load tester on group 31 batteries. And the carbon pile tester uses the same principle as the load tester show. I used the cell tester like the one shown 70 years ago. And it would still trust it to load test a cell.