Confused about the flow rate and pressure drop relationship measured across the orifice

Im actually so confused about how a small amount of pressure drop across the restictiction can allow the FT to read the total flow rate across the pipeline

As i know increase in pressure drop causes increase in flow rate as per the equation Q = K √(P) . If this is the case, then the flow rate across every parts that has fittings or valves which has different amount of pressure drop will also lead to different amount of flow rate? But theoretically i know that the flow rate across the line be the same.

Or is it related to calibration in the flow transmitter? Like a certain amount of pressure drop will lead to a certain amount of flow rate according to the kfactor, K? Please help.
Any restriction in the pipe (roughness of the pipe, valves, fittings like elbows and tees, orifice plates, etc.) will cause a reduction in the flow of the entire line, but the flow will be constant throughout the line. In other words, say you have 1000 l/m flowing through a pipe system. If you add a valve to the system (or partially close an existing valve), you've added a flow restriction and will have a reduction in flow if all else remains equal (it never does, but still). SO instead of 1000 l/m, the pipe system may see 995 l/m.

If you're electrically inclined, think of Kirchhoff's current law. In a series connection of devices, all devices will see the same current (flow) but not necessarily the same voltage (pressure drop). Adding resistance to a circuit branch will reduce the current in the branch, but every component in the branch will see the same current as every other component in the branch.

In an electrical circuit, it's not unusual to insert a small resistor (like 1Ω or less) and measure the voltage across it to determine the current in the circuit. That's basically what your flow transmitter is doing. It's measuring the pressure drop across the orifice and is calibrated to convert that to flow rate for the particular fluid that's flowing.
joseph, you can include all those concern in your meter calculations. The math is well documented in various standards, and in reference books.
If Flow rate remains the same then why does delta P have a proportional relationship with Q, flow rate? Q = K √(P). My understanding is that Q increases with pressure drop, im confused.