I got the colony counter from scienceware (F37862-0000) if you actually need to keep a running count of your dots. More expensive than a marker but it prevents cramped thumbs from the bus driver clickers we had before. Sylvia Sylvia P. Poulos USDA-ARS-Animal Physiology Research Unit Athens, GA 30605 706-583-8279 706-542-0399 (fax)