This lecture covers various techniques for fluid velocity measurements, including piv, pitot tube, hot-wire, and optical measurement techniques. It delves into the principles behind rotating mechanical flow meters, pressure-based velocity measurements using Bernoulli's equation and Pitot tubes, thermal anemometry with hot-wire probes, and particle-based velocimetry such as laser Doppler anemometry and particle image velocimetry. The lecture also discusses calibration, timescales, cross-correlation in PIV, and advanced correlation techniques like windowing and peak fitting. Additionally, it explores stereo particle image velocimetry and provides an overview of different measurement techniques.