The reason that Astro.com and our app get different results is that we use different methods.
There are different methods that are used to calculate the progressed ascendant from the progressed MC. Astrodienst uses one and we use another, but neither one is considered wrong. Dieter Koch, the chief programmer at astro.com explains how their method of calculating the progressed ascendant differs from ours. It is pretty technical. We can summarize as follows: When we calculate the progressed ascendant, by secondary progression, we use a method that is quite standard amongst all astrologers. First, we progress the MC by the solar arc for the desired date (this is the distance that the Sun travels from its birth location by secondary progression). Then we calculate the progr Asc. from that MC. A letter that I have from astro.com indicates that they use a different method, as described in their Help text on how the calculation is performed. That method results in a different value for the progressed ascendant. We believe that the calculation that we use, from the progressed MC, is the most universally standard method.