I've been using pendulum for many years now (over 15).  
Let's say that I know it a little bit  
What I'm writing now, is absolutely My experience with it and nothing more.

Believe me, it can be amazingly accurate and helpful!

I have to say that I rarely got wrong answers and this happened when I was not relaxed
or completely "neutral" while I was asking my question.
Being neutral, so as not to affect the pendulum's answer.
This is a very delicate point, as it's very easy to get  a wrong answer that we deeply wish and not
the right answer that we probably dislike.
But this is only a matter of time and practice. And will, of course!

I have totally 3 pendulums, each one dedicated to a different subject.
The first was bought, the other two were made by me.

The first is used for health questions.
The second is used for sentimental questions
The third is used for general questions.

Throughout the years, I found a simple way to get more clear answers.
I simply write down on a paper all the possible answers to a question, plus the option "something else",
in case that the right answer is not included on this paper.
It works great!

The first time that I tried to see how my pendulum responses I used the Free method.  
I actually wanted to see IF and how it works with me.
I just asked it to show me which is Yes - No - I don't know yet - I don't want to asnwer.
After that, I checked it by asking simple questions.

So, my pendulum is moving forward-backward for "Yes".
Right - left - right - left for "No"
Clockwise cycles (from right to left) for "I don't know yet".
Opposite clockwise cycles (from left to right) for "I don't want to answer".

And if it's not moving at all (something very rare), there are 3 possibilities
in this order:
1. The specific pendulum doesn't suit me.
2. It's not the right time to ask or I'm very negative inside.
3. I'm not concentrated enough.

Finally, what I really know now is that the more I use it, the more it helps me.