Patent ID: 7517694

Claim:
A method for performing an optical read of dead volume of fluid in a metering tip, said tip containing a volume of aspirated fluid, a portion of said fluid being dispensed as samples, said tip comprising at least one stepped area within an interior of said tip, said at least one stepped area including a sharp diametrical edge, said method including the steps of: i) dispensing samples from the volume of aspirated fluid from said metering tip through a lower tip opening; ii) aspirating an air bubble into said tip, thereby drawing the remaining fluid retained in said metering tip upwardly and into a cylindrical section of said metering tip, said cylindrical portion being defined with a substantially constant planar internal diameter defining a read window wherein said at least one stepped area is located above said read window, wherein said stepped area flattens the upper meniscus of said retained volume of fluid; iii) sealing the lower tip opening of said metering tip; and iv) optically reading the retained volume through said defined read window.