Final answer:
The finger reckoning method involves using fingers for counting and calculations, but a specific method for multiplying 5 by 6 using finger reckoning isn't provided in the question. Additional context or information would be necessary to explain it in more detail. Historical references offered do not give a direct explanation for the finger reckoning method.
Step-by-step explanation:
The question relates to the finger reckoning method, which is a manual technique used from ancient times for counting and simple calculations. This method involves using fingers to keep track of counts or numbers as one performs calculations. However, the description provided does not give a clear method for multiplying 5 by 6 using finger reckoning.
To multiply 5 by 6 using fingers in a traditional way, one could simply count up to 5 on one hand and then repeat this count 6 times using the other hand or by recounting the first hand repeatedly, though this is a basic and non-specific technique.
Considering the objective to explain a method for 5 x 6 using the finger reckoning method, additional details or historical context would be necessary to provide a specific step-by-step explanation. The information given, such as references to knuckle mnemonics for the number of days in a month or measures of lengths on a Nilometer, suggests a complex historical context which is not directly related to the method of finger reckoning being asked about.