What is the most accurate method of calculating a respiratory rate?

What is the most accurate method of calculating a respiratory rate?
a) Counting the number of respiratory cycles in 15 seconds and multiplying by 4.
b) Counting the number of respiratory cycles in 1 minute. One cycle is equal to the complete rise and fall of the patient’s chest.
c) Not telling the patient as this may make them conscious of their breathing pattern and influence the accuracy of the rate.
d) Placing your hand on the patient’s chest and counting the number of respiratory cycles in 30 seconds and multiplying by 2.