While deciding the unit for heat, which temperature interval is chosen ? Why ?

Explanation

While deciding the unit for heat, the temperature interval chosen is `14.5 ^(@)C ` to `15.5 ^(@)C ` .
If we heat 1kg of water by `1^(@)C ` in different temperature range than than `14.5^(@)C ` to `15.5^(@)C `, the amount of heat required is slightly different . It is, therefore, essential to define a specific temperature range while defining the unit of heat.