A chart which is partly factual and partly impressionistic consists of a 12 hour clock divided into parts. Each part is a particular color. Some colors are the same as on the Time Line of Life. The colors are significant here. Black indicates the absence of knowledge, yellow for the dawning of life, blue for water, brown for land, green for vegetation and life, red for something new.
The Clock of Eras is factual as it gives the duration of time of the eras and also a scale in terms of years. These are shown in the key/legend. The duration of time contained in the different eras is shown on the clock and in the key/legend in hours, minutes and seconds. The number of years is only shown in the key/legend.
The 12 hours represents 3,000,000,000 years and one hour represents 250,000,000 years.