Measuring Maximum and Minimum
If possible it is best to record the daily maximum and minimum temperature as well as that which you record at a specific moment in time when you make your observations.

You can simply use your normal thermometer. With this you need to record temperatures at about 14:00 where the daily maximum usually occurs, or very early morning when the temperature is similar to the overnight minimum. These are good times to take your am/pm measurements.

Special Max/Min Thermometers
Otherwise, a special maximum and minimum thermometer actually records the highest and lowest temperatures during a particular time period, usually one day. There are two types - the liquid in glass type (known as 'Six's thermometer') has little tiny metal markers inside the tube which are pushed around by the liquid and read against a scale. The bimetallic dial type has pointers which are very easy to read. Both need to be reset after every reading.