It’s not quite calculus, but it’s getting pretty close with all options Congress has added to the federal crop insurance program—now the biggest part of the safety net for American farmers, according to Politico.

The newest refinement is yield exclusion (YE). It’s a provision of the 2014 Farm Bill added on the behalf of farmers in the South and West, who suffered due to recent severe droughts.

YE allows growers to exclude those especially bad years, which lowers their production score, in calculating what level of revenue protection they can buy. It has growers doing their math with the many variables in play, each impacting the optimal outcome.

Among the qualified counties, preliminary data recently released by the Risk Management Agency (RMA) shows that about 19 percent of the policies sold thus far have taken advantage of the new provision.