The arcsinh is a transformation we use in Cytobank for displaying digital data.  It is a generalized version of the biexponential transform you see in other software.  The reason for this stems from the fact that flow cytometry data has traditionally been shown on a log scale (e.g. data from calibur) but  facs data from a digital machine (e.g. lsrII) can have negative numbers.  Our current mathematical laws don't allow taking the log of a negative number so we have to use a different transform that keeps the region linear around 0 and log like as we get towards positive and negative infinity.

Arcsinh values are calculated by applying the arcsinh equation divided by a "cofactor" to the measured intensity value.  The "cofactor"  defines the size of the linear region around 0. The smaller the cofactor the bigger the linear region. There are a few places you can adjust the defaults for this in Cytobank.  One is in the plot settings button on the gating applet and two is on the illustration page.  You can get the same answer in Excel by taking an intensity value and using the function ASINH.  The syntax is "ASINH(value/cofactor)".