This paper investigates the interplay of words and expressions with students' efforts to indicate times on a clock. We consider how elementary students interpret precise times (e.g., 2:30, 4:30) as compared to relative times (e.g., half past 11) as they describe this intangible quantity using a clock. Interviews with students in grades 2 and 4 (n = 42) revealed that precise times led to whole number descriptions whereas relative times led to descriptions of part-whole relations consistent with representations of measure. A subsequent analysis of assessment performance of students across elementary grades (N = 612) corroborates the differential performance based on expression used in the tasks. Findings suggest that elementary students need further support to treat this invisible quantity according to measurement properties. Implications for theory are discussed. [For the complete proceedings, see ED606556.]