Gauge

ijk

(a semi-norm; a function that assigns a non-negative size to all vectors in a vector space)

meetinstrument

(any instrument for ascertaining or regulating the level, state, dimensions or forms of things; as, a rain gauge; a steam gauge)

meter

(a measure; a standard of measure; an instrument to determine dimensions, distance, or capacity; a standard)

inschatten

(to estimate)

meten

(measure)