Patent ID: 7472667

Claim:
A period indicator comprising a liquid-permeable substrate and an indicative section which is overlaid on a portion of the substrate and which is formed from a liquid-permeable material having a low light refractive index, the indicator containing a volatile liquid, wherein the indicative section is formed by coating a surface of the substrate with an indicative-section-forming material prepared by mixing a binder and finely divided particulate matter having a low light refractive index, the indicative section comprises two or more regions, including a first region and a second region, and the regions differ in height from one another as measured from the surface of the substrate, as coating amounts per unit area of the indicative section forming material in the two or more regions differ from one another, wherein the first region is higher than the second region as measured from the surface of the substrate, so that the two or more regions develop signs with a time lag, wherein the sign in the first region is developed quicker than the sign in the second region, providing stepwise indication with respect to the quantity of residual liquid.