Once you have created a Global DB, you need to define the parameters that will be a part of that block. I assume you created a parameter called Weight. It sounds like you want to store a number of weight values, so you would give the parameter "Weight" a data type of "Array[lo..hi] of type...", and then define the array data type as Real with, for example, 50 values, so it would be configured as 0..50.
Let me assume the data block is called Weight_Data and that the parameter you created is called Weight, and this is an array of Real values. In that case, you can read or write from index 4 of the array with the format: