The 5851A is a PAL vectorscope manufactured using the latest advances in engineering and ergonomics design. The 5851A is a PAL vectorscope manufactured using the latest advances in engineering and ergonomics design. It provides a convenient method for observing and measuring the relative phase and amplitude of chrominance signal components. In addition to the internally etched graticule, it utilizes a unique patented technique which electronically displays the error limit boxes. This improves the accuracy of phase and amplitude adjustments by eliminating errors due to CRT non-linearities. It provides three loop-through inputs, a Z-axis blanking input test circle pattern and 100% or 75% amplitude selection is provided.