Other ways include dollars spent or results achieved. A step is not a date. A step is an interval of time in which money is spent, events occur or results are recorded. The interval may be two weeks, two months or two years. A good research and development programme should contain both steps and milestones.
Businesses run on business cycles.
They may be monthly cycles, seasonal cycles or annual cycles. Research projects run on event cycles. These cycles have nothing whatsoever to do with regular time or repetition. A research project is no different than a construction project. Steps and milestones are arbitrarily imposed.