Yes, got that, and SD does ask you your altitude. But, without the OAT, I don't see how SD could make convert IAS to TAS, and TAS is surely what you need for the PLOG calculations.
Just to add another element to the original question, the layout of the SD PLOG also seems to show that conversion from degrees true to degrees magnetic before applying the wind - whereas the wind vector is also stated with degrees true. However, just because that's the layout of the PLOG doesn't mean the calculation workds in that order I guess.
But, it's the ground speed calc which is foxing me.