adding problem

[merpus 0]

hey I am fairly new to all this i have a good grasp on things but I am finding I am having trouble with a few terms and cannot add items like full seachest 

    
    <event name="SeaChest">
        <pos x="3729.52" z="6008.87" a="-1" />
        <pos x="3678.97" z="6001.09" a="-1" />
        <pos x="3712.51" z="5973.38" a="-1" />
    </event>

 

a="-1" />

this is where i am confused i have seen where these numbers are changed and do not understand please if anyone can assist in my head not doing itself in would be kindly appreciated