For near visual acuity, 1M is twice as small as which notation?

For near visual acuity, 1M is twice as small as which notation?

• A. 2M
• B. 1M
• C. 3M
• D. 0.5M

Answer: (A)

In near vision testing, M notation expresses letter size by the angular size the letter subtends at a standard viewing distance. A 1 M letter is defined so that it subtends a fixed small angle (5 arc minutes) at 1 meter. When you increase the M value, the letter size increases proportionally. Doubling the M value makes the letter twice as tall and its angular size at the same distance twice as large. Therefore, 1 M is half the size of the notation that is twice as large. The other options would be the same size, smaller, or larger by more than a factor of two, which doesn’t meet “twice as small.”

In near vision testing, M notation expresses letter size by the angular size the letter subtends at a standard viewing distance. A 1 M letter is defined so that it subtends a fixed small angle (5 arc minutes) at 1 meter. When you increase the M value, the letter size increases proportionally. Doubling the M value makes the letter twice as tall and its angular size at the same distance twice as large. Therefore, 1 M is half the size of the notation that is twice as large. The other options would be the same size, smaller, or larger by more than a factor of two, which doesn’t meet “twice as small.”