The modeling approach and associated software PRIMELT3 (Herzberg & Asimow, 2015) were designed to invert primitive basalt compositions for the primary magma composition, the 1 atm olivine liquidus temperature of the primary magma, and the mantle potential temperature at which the primary magma would be generated by batch or accumulated fractional melting of peridotite. Its successor PRIMELT3-P has the same strengths and limitations. It is restricted to primitive basalts that differ from their primary magmas only due to olivine addition or subtraction; this excludes most basalts, which have generally also fractionated plagioclase and clinopyroxene. Successful solutions are only possible for primary magmas derived from a nominally anhydrous fertile peridotite source, not from pyroxenite or from volatile-rich peridotite sources. Each of these restrictions has been documented in detail (Herzberg & Asimow, 2008 and the software provides tests and flags that recognize and warn the user when the model is being misapplied.