Products for measuring length while viewing objects under magnification

Loupes

There are many products that are a loupe with an integrated scale.

Microscope slides — The cheapest

These are widely available from many different channels.

• AmScope
• Amazon searches:   [1] [2] [3]

< $100

Usually clear plastic.

• Lithco — Transparent ruler with a resolution of 0.1 mm, it's resold by many places.
• BoliOptics
• (search at Google Shopping)

$100 to $1000

• Edmund Optics
• Graticles Optics
• Ted Pella
• various sold by MicroscopeWorld (though a few are > $1000 and/or NIST certified)

> $1000 but not NIST-traceable

• PeplerOptics glass rulers — The graduations are chrome-plated.

> $1000     NIST-certified or NIST-traceable

• sold by MicroscopeWorld
  • a few that are > $2000
• Geller [1] [2]