A differential manometer as shown in the figure below is used to measure the difference in pressure at points A and B in terms of the specific weight of water, w. The specific gravities of the liquids X, Y and Z are respectively S1, S2, and S3.The correct difference \(\left( {\frac{{{p_A}}}{w} - \frac{{{p_B}}}{w}} \right)\) is given by

• A. h3S2 – h1S1 + h2S3
• B. h1S1 + h2S3 – h3S2
• C. h3S1 – h1S2 + h2S3
• D. h1S1 + h2S2 – h3S3