Phycotech Utermöhl Chambers: 42.85mm x 88.9mm Used on an inverted microscope Counting through a round-replaceable 25mm cover slip Different size towers hold various volumes Two-piece assembly, slide tower off and replace with cover slip Tower can be removed from chamber surface without disturbing chamber contents The two-piece assembly allows you to remove the tower and replace it with a cover slip. This makes the counting assembly more stable, easier to manipulate, and allows for variable volumes (5+, 10+, 25+, 50+, 100+mL*). When the H:D ratio is greater than 5, currents can occur within the tower and prevent proper settling. The H:D ratio is greater than 5 in the 50+mL and the 100+mL towers. Also, the 100+mL tower assembly includes a brass weight to hold the seal. The customer needs to decide which tower size is appropriate for their application. Instructions for use (PDF format): PhycoTech Utermöhl Chamber Tips & Hints Using the Blank Base Plate *Please note that all of the sizes listed have a + sign immediately following the size indicated. These towers are not graduated, and will hold more than is actually noted. In our experience, we've found that having the extra volume available can be beneficial. Therefore, we have allowed for extra sample in each tower. For example, the 25+mL tower holds approximately 30mL. We recommend using DOW CORNING® high vacuum grease as the preferred vacuum grease for tower assemblage.