The ruler represented on this simlulator is in fractional inch (fractionated). This means that the numbering graved in the line gauge represents one inch that was subdivided in sucessive halves until the fraction of 1/16" (one sixteen avos of inch).
Observe in the simulator that is not possible to be sure about how much the mensuring border is in the marks. technological devices how the vernier correct this limitation.
Observe also that is not possible to be sure about if the mark is trully aligned with the mensuring border in both sides. This imprecision of reading has as consequence that the measure taken is not much trustfull or is not correct. Instruments as the vernier caliper correct this limitation.
Take a look in the page:
Use the measures in fractional inch - comprehending and aplying