Greetings to our friends in South Africa! There’s a few visual-type methods that I have to admit is sourced from delishably.com to see if oil is ready for frying. The first  method (which I found in several other sources as well) is to carefully dip the tip of the handle of a wooden spoon into the heated oil. If the oil begins to steadily bubble, then the oil is good to proceed. If the oil bubbles very vigorously, then the oil is too hot. If no or few bubbles occur, then the oil is not hot enough.

The second method suggested is to drop a 1” bread square into the oil. If it takes a minute to brown, the oil is good for frying.

And the third, most curious method is to drop a single kernel of popcorn into the hot oil. The kernel will pop at 350-360°F degrees which is just right for potato frying. The best method of all? Use a thermometer. :)