If a book reports units of "30g/Nm3" tar produced - what does that mean? I think it means there are 30 grams of tar per cubic meter of gas. But what does the 'N' mean? Thanks for any help. Frank -- Frank Shields Soil Control Lab 42 Hangar way Watsonville, CA 95076 (831) 724-5422 tel (831) 724-3188 fax frank at compostlab.com www.compostlab.com