Numerical prefixes are not restricted to denoting integers. Numerical marking is the manner of denoting the arithmetical values of contour lines. The menus were not marked with a symbol denoting the command key. Exa is a decimal unit prefix in the metric system denoting 10 or . The symbol 0 for denoting zero is a variation of this character. Some systems also use ideograms, symbols denoting abstract concepts. Each of these affixes are denoting a transitive relationship between two things. The lower and upper bound are expressions denoting integers. His defining characteristic is his glasses, which are drawn with swirls denoting their thickness. This leads to several groups of vowel letters denoting identical sounds today. The line was marked in intervals with flags denoting depth. The Mordvin word "mirde" denoting a husband or spouse is traced to the same origin. Many characters have multiple readings, with instances denoting different morphemes, sometimes with different pronunciations. It was originally given the designation XBLR-2 ("XBLR" denoting "Experimental Bomber Long Range"). Various compound constructions exist for denoting past habitual action.