Asymmetric Systematic Errors

Asymmetric systematic errors arise when there is a non-linear dependence of a result on a nuisance parameter. Their combination is traditionally done by adding positive and negative deviations separately in quadrature. There is no sound justification for this, and it is shown that indeed it is sometimes clearly inappropriate. Consistent techniques are given for this combination of errors, and also for evaluating $\chi^2$, and for forming weighted sums.