This is the temperature of the egg before it is cooked. This will depend on whether you prefer to keep your eggs in the fridge or at room temperature
This is the temperature that the boundary of the yolk will be at after cooking for the indicated time.
At 66°C nearly all the white is set and only the outer edges of the yolk are set, perfect for dipping soldiers.
At 80°C-90°C is the temperature at which the yolk changes from a waxy texture to the crumbly texture typical of hard boiled eggs.
Typically we use boiling water to cook eggs. Boiling water is typically 100°C at standard atmospheric pressure. However it can change due to weather or being at higher altitudes.
If you want to sous-vide your eggs it may be better to use a temperature below 100°C. Such as 85°C.
This is simply how big your egg is, weighing the egg is much more accurate than trying to measure its size.
If you intend to cook more than one egg select eggs of similar mass and cook them all using the average mass.
If you would like to learn more about soft boiled eggs here is the link that inspired me to create this calculator. Towards the perfect soft boiled egg.