Invisible Line / tapeline

People should check the scale and record or remember the length meticulously when they usually use a tapeline. But, to measure a length exactly, there are limits on checking the scale. So I propose a tapeline without a scale. This tapeline displays only the length that we want to know and the scale of the length that we measure. If you pull the string of a tapeline, you can find an exact length on the display of the tapeline, needless to check the scale. In addition, you can mark necessary unit-specific length on the tapeline.