What is the formula for calculating the length of the scale?

• A. Minimum length to be measured x R.F.
• B. Minimum length to be measured ‚Äö√†√∂‚Äö√†√´ R.F.
• C. Maximum length to be measured ‚Äö√†√∂‚Äö√†√´ R.F.
• D. Maximum length to be measured x R.F.