For a non-chemist the most attractive method of quoting the improvement might be "a decrease of X unit cost per kilogram of compound Y". This, however, would be an over-simplification—for example, it would not allow a chemist to visualize the improvement made or to understand changes in material toxicity and process hazards. For yield improvements and selectivity increases, simple percentages are suitable, but this simplistic approach may not always be appropriate. For example, when a highly pyrophoric reagent is replaced by a benign one, a numerical value is difficult to assign but the improvement is obvious, if all other factors are similar.