Fsc-a

Symptoms: A flat line at the top of the plot; populations look "squished." Cause: Gain is too high. Solution: Use beads (e.g., 3µm and 6µm) to set voltages. For most cells (3-15µm), start with FSC voltage at ~50-100V on analyzers (e.g., BD LSRFortessa). Never use automatic FSC gain on unknown samples – it will ruin relative size comparisons.

Imagine a sensor counting cars driving over a single-lane bridge. A smart car gives a small signal. A semi-truck gives a big signal. But what happens when two motorcycles drive side-by-side? The sensor sees a wide signal and records it as one "wide truck." Your data is now wrong. Symptoms: A flat line at the top of

In flow cytometry, this is a doublet (two cells passing through the laser beam at the same time). If you don't remove doublets, you will think your cells are bigger and have twice the DNA content than they actually do. Never use automatic FSC gain on unknown samples

If two small lymphocytes pass through the laser simultaneously, the instrument may interpret them as a single event. This results in erroneous data interpretation—specifically, the DNA content or fluorescence intensity will appear artificially doubled. A semi-truck gives a big signal