How hard to smack the object?

The wonderful Christine M left me a comment with this question.

Ms Scarlet
I have always avoided spanking the penis out of fear of serious bruising, knowing there are so many blood vessels within. Can I therefore enquire, when you use the ruler, can you give an indication of how hard you strike, and what might be a typical number of strokes? This is not mentioned in your Manual, which I have enjoyed.
At the end, is there much bruising, and if so, how long does it last?

This is my response below. Do any other ruler smacking users have any guidance tips on how hard to smack?

It is hard to put into the written word how hard a smack should be. I can tell you that there is never any bruising afterwards as a result. I smack at least until the penis has been turned a shade of pink compared to its normal colour. As far as I can tell, if smacking with the force required for that, there is no limit to the number of smacks that can be applied. Quite a good smacking method, is two light taps followed by a serious ‘tap’. Then repeat that sequence of three – again, and again and again. A good way to judge the right force for the smacks is to experiment by smacking your own inner thigh or inner wrist. (Not in front of your sub). I have had many guests apply smacking and I do so at least twice a week, and there has never been any damage. I find a good smacking force causes whimpering and pleading, especially when applied to an already smacked-sore, pink penis, but does not cause shouting out or screaming. Please let me know how your first session goes and what if any of what I have written is helpful. I will then include any that is in edition 2 of my Manual at some point.