These are the mechanical specifications for the HP Designjet Z2100 with inline spectrophotometer for color bar artwork:

• The printable area of the media defines the maximum length of the color bar.
• Minimum patch width in the scan direction: 15 mm (0.59 in.)
• Minimum patch height: 15 mm (0.59 in.)
• Recommended gap between rows and columns to reduce color bleed between adjacent color patches: 0.5 mm (0.020 in.)
• The inline spectrophotometer has no requirements for the color of adjacent patches because it is a spot measurement device, not a strip reading device.
  For example, adjacent colors need not have high contrast.

Note: Color bars for the HP Designjet Z2100 proofer with inline spectrophotometer can have multiple rows of color patches.