Which is the arithmetic check for the height of instrument method?

• A. ∑FS + ∑BS = First RL + Last [email protected]
• B. ∑BS – ∑FS = Last RL – First [email protected]
• C. ∑FS + ∑BS = Last RL + First [email protected]
• D. ∑BS – ∑FS = First RL – Last [email protected]