To know the value of a mentor we need to define what it is.
The dictionary states:
1 His political mentors: adviser, guide, guru, counselor, consultant; confidant(e).
2 Regular meetings between mentor and trainee: trainer, teacher, tutor, instructor.
From these definitions we can see that a mentor is really more than a teacher, guru, adviser or guide. A mentor is a combination of all of the character traits listed in the definition and more. A true mentor is focused on the the success or positive outcome for his follower. They want the best for those who are in their care or seek their advise.
The value of a great mentor really can not be quantified. The mentors value is only really fully understood by the person who puts the mentors teaching into practice. Then with the benefit of time and introspection by the pupil the mentors value is discovered.
The challenge for us is finding a great mentor who really cares about us and our success.