Gear oil dip stick shows hot and cold levels, what does this indicate.?

How often spark plugs to be changed (corolla 2002).Gear oil dip stick shows hot and cold levels, what does this indicate.?
The oil dipstick has two markings. 1 is for hot and 1 is for cold. These are used to determine accurate readings. The cold reading is used for when you have left your car for a long while and the engine has cooled down. The oil level should be at the full level of the cold reading. The hot level is used to determine your oil if you have been running your car. For example, you drive and stop at a gas station to check your oil. Since the car engine is hot, you cannot get an accurate cold reading. So hot is used which is usually a maximum fill line as the oil is being circulated and has expanded. In this case you do not want to go over the hot fill line. Hope this helps.Gear oil dip stick shows hot and cold levels, what does this indicate.?
Change plugs when dip stick shows cold!!