The Stovall Well Mark marks a researcher’s place in 96 and 384-well plates to help remedy failed reactions and costly repeats caused by distractions and interruptions. The unit consists of a windowed frame which locks any skirted or un-skirted well plate in place; a moving, protective shield with an open slot revealing one column of wells at a time; a single well isolator with protective skirt which moves down a column one well at a time; and laser etched letters and numbers on the index shafts to clearly indicate position. At beta site labs, commercial and academic, errors were reduced by 26% and 32% respectively within a two week period.