While doing CVP calibration, zeroing of the manometer should be done at which of the following levels?

Correct option is D

The phlebostatic axis is the reference point for zeroing the central venous pressure (CVP) manometer. It is located at the level of the right atrium, which is typically at the fourth intercostal space, mid-axillary line.
Explanation of options: (a) ✘ Incorrect. Erb's point is used for auscultation of heart sounds, not for CVP calibration. (b) ✘ Incorrect. Koch's point is related to the location of the atrioventricular node, not for zeroing the manometer. (c) ✘ Incorrect. Kauffman's point is not used in CVP calibration. (d) ✔ Correct. The phlebostatic axis is the correct reference point for zeroing the manometer in CVP measurement.