it’s under absd rules but the specific stamp duty pertains to 1st sinkie property an amerikano buys. it’s 4-5% depending on whether price is below $1.5m or over. that’s equivalent to buyer stamp duty (bsd) that a sinkie is subjected to. of course if amerikano buys 2nd property in sg he’s subjected to same sinkie absd. “a” means additional as in 2nd and subsequent properties. they are all sexplicitly sexplained on the iras site.