Since blood production requires iron, you should eat iron-rich foods for two weeks before your appointment. This will help you have strong blood for donation and help you better recuperate after your donation. Iron-rich foods include spinach, whole grains, fish, poultry, beans, organ meat, eggs, and beef.
To calculate the change in temperature, subtract the initial temperature from the final temperature. Example: 84.2 degree Fahrenheit - 41 degrees Fahrenheit = 43.2 degrees Fahrenheit. The temperature from morning to afternoon changed by 43.2 degrees Fahrenheit.
to answer the 2nd part. the scientific unit for measure of temperature is Kelvin (K), which starts at 0 (also known as absolute zero, or the lowest temperature possible). 1 unit of Kelvin = 1 unit of Celcius. So to convert a temperature from Kelvin to celcius, add 273.6, so 0 degrees celcius would equal 273.6 Kelvin. Now what is important to understand about temperature is that there is only HEAT (unit measured in Joules), there is nothing called COLDNESS etc.. so any temperature above absolute zero means that there is some amount of heat (Joules) present.