Universidad de Sevilla
Four clocks with 24h analog dial signaling latitude , the efficiency of noon insolation in summer, the permanent daytime (yellow), the permanent night time (red) and the alternating region (pink). Human activity starts between the winter sunrise (w) and the equinoctial sunrise 6am. DST regulations bring human activity one hour earlier in the spring transition: from w to w1, or from w1 to w2, or from w2 to w3. Clocks display mean solar time.