How does a turbine flow meter work and what affects its accuracy?

Turbine flow meters have a rotor that spins at a rate proportional to fluid velocity. Magnetic pickups detect blade passage, generating pulses converted to flow rate using K-factor (pulses per unit volume). Accuracy factors include: viscosity effects (need viscosity-compensated K-factor curves), flow profile (requires 10-20 pipe diameters upstream), bearing wear, and fluid cleanliness. High accuracy (0.25%) for custody transfer applications but require clean, lubricating fluids.