Every measurement includes uncertainty. the rightmost digit of any quality is always estimated: 1. 0052 the underlined 2 is the estimated digit the measurement device used determines the number of significant digits possible. Determinig which digits are significant all non-zero digits zeros between 2 non-zero numbers are significant: 5. 004, zeros that end in a number beofr or after a decimal point are significant. 13. 80 or 4. 00: zeros to the left of a number are not significant. They only serve tp place the decimal point. 0. 003: zeros that end a number without a decimal point are generally not consided significant but can be ambiguous. They may be exact by definition: conversion factors. 60 min = 1 hr they may be exact by count: 26 letters in the alphabet. All measured qualities consist of 2 things: a number and a unit: units are manipulated by numbers. A conversion factor is a ratio of equivelant quantities used to express a quantity in different units.