Rise - Making markers appear across an image in order from left to right

I've been adding markers in a Rise course on a photo background, and want them to reveal from left to right when the small arrows which appear are used by the participant. At the moment, I have about 10 markers on the photo, but when the arrows are used on the markers to move to the next marker, they seem to open randomly. Is there are way of ensuring that the markers reveal from left to right? Is this to do with the order that the markers are added to the photo? I've added the photo so that you can see the arrows. Any help on this is much appreciated. 

5 Replies