1. A method of matching optical metrology tools in a fleet of optical metrology tools, the method comprising: a) obtaining a first set of hypothetical profiles of one or more structures, wherein the first set of hypothetical profiles was determined based on a first set of measured diffraction signals measured using a first optical metrology tool from the fleet of optical metrology tools; b) obtaining a second set of hypothetical profiles of the one or more structures, wherein the second set of hypothetical profiles was determined based on a second set of measured diffraction signals measured using a second optical metrology tool from the fleet of optical metrology tools; c) obtaining a reference profile; d) generating a first transform based on the first set of hypothetical profiles and the reference profile; e) generating a second transform based on the second set of hypothetical profiles and the reference profile; f) obtaining a first hypothetical profile, wherein the first hypothetical profile was determined using the first optical metrology tool; g) obtaining a second hypothetical profile, wherein the second hypothetical profile was determined using the second optical metrology tool; h) transforming the first hypothetical profile into a first transformed hypothetical profile using the first transform; and i) transforming the second hypothetical profile into a second transformed hypothetical profile using the second transform.