Alexandre Elder’s “Thermometer” function (cf. his writings such as “enter my trading floor”) allows to measure market strength, just as a thermometer does with temperature.
Ideally, I use it in daily charts, displayed as a uptrend / downtrend histogram.
REM Measure market strength
thermo = MAX((High[0] - High[1]),(Low[0] - Low[1]))
REM Returns 'Thermometer' value
RETURN Thermo