Most surgeons seem to say they can do safely achieve a density of 50-60 FU/cm². What I am wondering is does this number change depending on existing density, or is it static? If you already have 50 FU/cm² can they implant 50 more to give you a total density of 100 FU/cm², or is it a curve where the number of units that can be added is reduced by the amount of preexisting hair? My understanding is that there are two factors limiting transplant density. One is the size of the incision which has to be a set distance apart from each other. The other is the available blood supply. The former would seem to allow for implanting the same number of units regardless of the existing density, but perhaps not the latter.