What does VS stand for?

To have the same distance on the vertical scale representing equal percent changes, you can use logarithmic scaling.

The 32 articles work as chapters, covering the foundations (such as effective development, standards, contracting for test services, evidence-centered design, and preventing fraud), content (validity evidence, credentialing examinations) item development (computer item banking, editing and review, fairness), test design (practical issues, vertical scales, pass-fail tests), test protection and administration and post-test activities such as technical reporting and evaluation.

EXECUTIVE SUMMARY * GRAPHS IN CORPORATE ANNUAL REPORTS may have an altered vertical scale and often report a more favorable picture than warranted by the underlying financial information.