Complex sentence: Presentation of data on a logarithmic scale can be helpful when the data cover a large range of values--for the use of the logarithms of the values rather than the actual values reduces a wide range to a more manageable size.
Split into simpler sentences: Presentation of data on a logarithmic scale can be helpful when the data cover a large range of values. The use of the logarithms of the values rather than the actual values reduces a wide range to a more manageable size.