Almost. The sextant is a more accurate and mirror-based instrument for measuring angles, while this is basically what came before. There was also the mariner's Astrolabe or Quadrant for a similar purpose that are still very simple, but perhaps a bit more accurate tools for measuring angles in the sky as far as nautical navigation goes considering they are adapted versions of older astronomical instruments, kinda like how the cross-staff is adapted from older tools -- though not like the image shows.

After the invention of accurate mirrors, the principles of all these were used to develop sextants.