Price comparisons by weight shown incorrect

Love the website but there are problems with the way your prices are displayed as they are often incorrect when it comes to showing the price/weight comparison. For example if you search for 'frozen baked potatoes' the price is shown then for comparison the price per 100g is shown but is WRONG in most cases for the 800g bags listed. Can you explain why this is? Can you correct the miscalculation across all the products displayed please as it needs to be to maintain confidence in the site. Thanks