For about a decade it has been noticed from the measurements of many jets that the value of the preferred mode and the spreading rate vary within a range of about 100%. In the present paper it is suggested that extremely low‐levelspatiallycoherentdisturbances inindividualfacilitieschange the initial conditions of alaminarshear layer. The various initial conditions are able to cause different downstream developments of the jet and result in the discrepancies reported in the literature.