Since all assessed valuations are based on sales as of a certain date, later changes in the market will gradually make property assessments out of step with the real estate marketplace. The rise and fall of real estate values make certain properties more valuable or less valuable, in relation to each other. Doing a revaluation periodically brings the assessments into line quicker, and provides a correction to assessments when markets rise or lower. It makes the assessment of property taxes fairer, more accurate, and avoids the “sticker shock” that occurred when these projects were performed every 10 years or so.