The U-tube in a differential manometer is not inverted. It's actually upright, with both ends open to the atmosphere or to the pressures you're trying to measure.

Here's why the U-tube configuration works:

* Pressure difference: The purpose of a differential manometer is to measure the difference in pressure between two points.

* Fluid level change: When there's a pressure difference between the two points connected to the manometer, the fluid level in one arm of the U-tube will rise while the level in the other arm will fall. This difference in height directly relates to the pressure difference.

* U-tube shape: The U-shape allows for a clear visual representation of the fluid level difference. The difference in height between the two fluid levels is directly proportional to the pressure difference.

The key takeaway: The U-tube in a differential manometer is not inverted. It's designed to be upright so that the difference in fluid levels directly reflects the pressure difference between the two points being measured.