Welsh 
Top tips for making Measurements
Here are some helpful tips when making measurements of weather and climate.
To find out how to make a rain gauge, click here.
To
find out how to make a barometer, click here.
Temperature
Thermometers, rain gauges and other instruments should not be located close to buildings, though for security reasons they may have to be.
You need to measure air temperature, so make sure the sun does not shine on your thermometer. If you possibly can, you should place it in a louvred screen, i.e. a screen which has slats to allow the air to circulate around the thermometer. Do not place a thermometer too near a building, because walls retain heat. The walls can heat up the air nearby so that it is warmer than the air circulating over an open area.
If you are using a minimum thermometer, you must make sure it is not exposed to the sky at night. If it is, it will lose heat to space and thus give a temperature reading that is too low – maybe several degrees too low on a clear night. To measure the minimum air temperature, you need to shade the thermometer whilst still allowing air to circulate around it. Ideally, both maximum and minimum thermometers should be placed inside a louvred screen.
Rainfall
Do not place your rain gauge too near a wall, tree, hedge or fence as it will be too sheltered to catch the rainfall.
Wind gets funnelled between buildings and hedges and deflected when it flows around and over buildings and other obstacles.
Wind
To gauge wind direction, you need some
sort of indicator. This may be, for example, a home-made wind sock
or a flag or pointer on top of a pole or building. 
You can also use soap bubbles to indicate wind direction.
Ignore the movements of clouds; wind direction normally changes
with height.
You do not need equipment for measuring the strength of the wind. You can estimate the strength by means of the Beaufort Scale. All you need to do is observe the effects of the wind on leaves, dust, smoke, flags, etc. For an explanation, click on Beaufort Wind Scale for Land Areas.
If you have a device for measuring wind speed (called an anemometer), you can use the Beaufort Scale to convert speed to force.
Clouds
For assistance over cloud recognition, click on Cloud identification or The nature of clouds. If you would like to buy a cloud identification chart, which is a laminated card for use outside, click on Buy a cloudchart.
Automatic weather stations and electronic instruments
Care is needed when using automatic weather stations or electronic instruments (particularly electronic thermometers). Readings need to be checked and instruments well-calibrated..
Converting meteorological units
Two examples:
59°F = (59-32)x5/9 = 27x5/9 = 15°C.
20°C = (20x9/5)+32 = 36+32 = 68°F.
To convert a Fahrenheit temperature
reading to Celsius: first deduct 32 and then multiply the value
you get by 5/9.
To convert a Celsius temperature reading to Fahrenheit: first multiply
by 9/5 and then add 32.
To convert inches to millimetres
and vice versa:
1 inch = 25.4 mm and 1 mm = 0.03937 inch.
To convert barometric pressure
from inches or millimetres of mercury to millimetres:
millibars = inches x 33.8639, so 30 inches = 1015.9
mb and 1000 mb = 29.53 inches;
millibars = millimetres x 1.3332, so 760 mm = 1013.23 mb and
1000 mb = 750.1 mm.
Note that 1 millibar (MB) is equivalent to 1 hectopascal (hPa).
To convert wind-speed units:
[kt = knot; m/s = metres per second; kph = kilometres
per hour; mph = miles per hour]
1 kt = 0.515 m/s and 1 m/s = 1.94 kt;
1 kt = 1.853 kph, so 1 kph = 0.54 kt;
1 kt = 1.152 mph, so 1 mph = 0.87 kt.
Other Online guidance on weather observing
For an introduction, click on Weather observations. For detailed guidance, click on Watching the weather