The differences come in the calculation of your work. The easiest and most common method is to count the number of characters typed and multiply that by a per character amount. Your word processor program has a character count function. Other methods of calculating amount of work done is by line. Even if a line does not extend the full width of the page you are paid as if it did.
Some transcription services pay by the page or group of documents.
However it is calculated, the transcriptionist is paid by the amount of work typed. Medical transcription can be a very rewarding. You can choose whether to work at home or out of the home. You can be your own boss or become an employee of a transcription service. You can work during the day or during the evening.