In individual regions, this dating can be considerably refined; in Europe for example, Acheulean methods did not reach the continent until around 400 thousand years ago and in smaller study areas, the date ranges can be much shorter. Numerical dates can be misleading however, and it is common to associate examples of this early human tool industry with one or more glacial or interglacial periods or with a particular early species of human. The earliest user of Acheulean tools was "Homo ergaster" who first appeared about 1.8 million years ago. Some researchers prefer to call these users "early Homo erectus". Later forms of early humans also used Acheulean techniques and are described below.