C.44

Hi all, i'm absolutely not new to cars in any way but my "new-to-me" 2010 Citroen C3 just asked me top up the engine oil this morning. I went out to buy a 5 liter can of the same oil that's in it right now (as per the label attached to the engine) and wanted to top it off this evening. However, i can't figure out this dipstick! There are absolutely no markings on the plastic bit on the bottom at all http://sebastiaanswinkels.files.wordpress.com/2013/09/photo-e1378928851545.jpg Now i'm pretty sure it has to be somewhere inbetween the two holes but that's one heck of a margin. Can anyone help me out here? I'm not comfy putting 55miles / 80km on the clock every day without having it topped up asap.