yardstick

mittapuu, mittakeppi A measuring rod thirty-six inches long.
puhekieltä A standard to which other measurements or comparisons are judged.
2008 April 8, Michael R. Gordon and Eric Schmitt, “Attacks in Baghdad spiked in March, U.S. data show”, in wikipedia:International Herald Tribune|International Herald Tribune, 2008 April 8 edition, “Africa & Middle East” section,

Attacks against civilians in the capital remained relatively unchanged: 69 in March from 62 in February. ¶ However, another yardstick, the number of civilian deaths tracked by the Iraqi government, shot up last month after several months of decline.