Exercising outside in high temps can be a health hazard. Here's how to read your local index, according to a doctor, so you can stay safe.

All real-life graphs can be used to estimate or read-off values.The actual meaning of the values will depend on the labels and units shown on each axis. Sometimes: This graph shows the cost of petrol.

Plotting a graph takes time. Often mathematicians just want to know the key features. These are: shape, location and some key points (such as where the graph crosses the axes or turning points). So ...