How to modify the range_max's value of hokuyo LiDAR's parameters?

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Hello, I'm working in ROS kinetic.

I'm also using Hokuyo's LiDAR sensor and I'd like to modify some parameters concerning it.

In my understanding, urg_node.launch includes those things and I've tried changing.

But there are some queries,

1. I certainly set range_max parameter from default to 5.0 as the following code, but the published /scan topic has 5.59999 of /scan/range_max argument. Is that another code I have to modify?

    <param name="range_max" value="5.0"/>
   

2. The default setting(the setting that doesn't include any mentions concerning min or max angle) of the urg_node.launch file makes 726 rays and scan angle ranges from -120 to 120 degrees. However, when I set this min and max angle as -120 and 120, which is the same as the default setting, it only makes 684 rays, not 726. In other words, describing the angle setting resulted in the decrease of the number of the published rays. Why this happens??

All the code-file I worked on is only urg_node.launch and I think I need many things to get a desirable result..

Best regars