Measure wavelength across several wave gaps in a ripple tank and divide by their number. Determine frequency from counted oscillations over a timed interval, or use a known signal-generator frequency for a string. Calculate v = fλ; reduce parallax and timing uncertainty and repeat measurements. Tank ripples and string vibrations provide complementary methods. Example: State a string-wave control variable. Tension or mass per unit length when comparing frequency settings. Consider the conditions.