Print-out
The underlying math governing the distribution of colonies in a specific geometry is simple enough to encode on a piece of paper. To use this approach, just line up the colony-containing pipette tips with a printed ruler with markings specifying the expected position of a particular colony. The compiled Matlab App below can be used to generate rulers for cones with arbitrary lengths and volumes. Colony counting never looked so easy on paper.
How to do GVA on Paper
An ideal approach for field data, low resource settings, or STEM education, this approach estimates the number of colonies in the sample based on the position of the X colony from the tip, where X > 3. The more colonies counted the more accuate the result, but with diminishing improvements. In general finding the position of the 10th colony is sufficient to usually be within a factor of 2 of the correct value. Using a magnifying glass can help increase the dynamic range by allowing the visualization of colonies too small to count by eye.