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Minor progressions are progressions with the time key of a month for a year. This means that the minor progressed Moon has the speed of the transiting Sun. Therefore, on your 40th solar return, for example, you experience your 40th lunar return in minor progression.
I don't think they are worth the trouble, to be honest.

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the easiest way to calculate them is with an astro software program that will do it for you!

i use minor progressions and ruud66 has explained what they are... i mostly use solar arc directions, but i do look at minor progressions and find they often coincide with what is going on with a person - me anyway!