Excel Graphs

Hi there

I am producing a simple bar chart graph in excel. This is very simple data with only one column. However i would like to put a series of lines horizontally across the graph to show a high point, low point and average point i.e I will be able to see on the graph how my data column compares to the 'highest point of data, lowest point of data and average data mark' which are mentioned elsewhere in my document.

is this possible?

Please help

Many thanks

Esther