The Thermometer.

This is one of the most important pieces of kit in the darkroom. As already mentioned temperature is one of the main controlling factors in the processing of your films and prints. It is important that you have good quality thermometers that are graduated to at least half a degree but a quarter of a degree is better and one that has a thicker line at the vital 20 degrees C. It is a good idea to have a thermometer for each of the chemicals you use in the processing of your films and prints as it will stop cross contamination.Also there will be no hold ups if you break one. It is recommended that you keep to one type, preferably alcohol as it is safer than mercury. If a mercury thermometer breaks it will contaminate the chemicals it comes into contact with and fog any prints that are being processed at the time.

What temperature?

20 degrees centigrade is the standard temperature that film development should be carried out at. It is also important that this temperature be maintained throughout the process. You may use a higher or lower temperature which will shorten or lengthen the development time. There is a risk that the negatives may not be fully developed; you should wherever possible follow the instructions as to time and temperature unless an alternative has been suggested by those instructions. With experience you will know what temperature and time combinations give good results. I personally always develop my film at 20 degrees C unless a higher or lower temperature is recommended.