5．単位を意味するとき
◎ キロ当り http://www.sunsonline.org/trade/process/followup/1998/10270298.htm
The petition drive, which got underway Thursday, is protesting the resolution, which set a new reference price for imported denim pants at 23 dollars a kilo,(1キロ当り23ドル) compared to previous estimates of five dollars.
◎ メーター当り
It cost 5 dollars a meter.（それは１メートル当り５ドルだった）
◎ 一日当り～回
Shifting Saddam
U.S. Gen: Crumbling Support Network Forcing Saddam to Move More Often
The Associated Press
T I K R I T, Iraq, Aug. 7— Saddam Hussein has been forced to move at least three times a day（１日当り3回） because of mounting raids by U.S. forces on sites where soldiers have found evidence that someone important — perhaps the ousted Iraqi leader himself — had been hiding, a U.S. general said today.
A cheetah can run approximately 100 km/hr and a gazelle at 80.0 km/hr. (チーターは時速約100キロ、ガゼルは時速約80キロで走ることができる)
*) このように不定冠詞は、単位を表すことができます。これはperで置き換えることも可能です。A cheetah can run approximately 100km per hour.というように。