Time was first proposed as a quality control parameter by Watson. IN the above example the DNA histogram (Top left) appears to have an abnormal G0-G1 population. By collecting time as a parameter, an observation can be made as to the rate of cell collection. As can be seen at the right of this histogram, the collection rate appears to have been significantly reduced at region B. This may have been caused by a blockage in the flow cell or some other non-biological problem. If this caused turbulence in the flow cell, a significant impact might be seen on the CV of the fluorescence histogram. By removing the data collected during the time gate B (by using a Boolean operator [a NOT B], only data collected at the appropriate rate is included in the data analysis as seen on the lower left histogram. A normal time histogram is shown on the lower right.
