1 PS (PferdeStarke) = 0.986 Bhp
1 Kw (kilowatt ) = 1.341 Bhp
PS is the metric version ( well German version ) of Bhp
ok now lets see if i get this right
1 hp = 550 ft/lb
1 PS = 75 Kg / meter
550 ft/lb = 76.07 kg/m
so Ps is just a nice rounded figure using the work done to find the power figure
found a converter here
http://locost7.info/converter.php