What do fraction marks mean?

I have learnt such a lot since I joined this forum, now i am investigating fraction marks, but don't know what they mean. I have seen a few pieces with only fraction marks and no impressed number, sometimes with a date. What do they mean? Were they before the numbering system started?
For instance this vase on Trade Me [You must be registered and logged in to see this link.] is the same shape vase as below
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and this vase has a different number on the base
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and this vase has on the base
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and the stamp
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Any help appreciated

most often the fraction number was a way of keeping track of the glaze that went on the piece so that the "ingredients" could be replicated to make similar glazed pieces. kinda like a recipe.

As a potter those early Ambrico glazes really fascinate me.
They appear to have used three different glazes to create those wonderful triple glaze effects.
The base glaze that would firstly cover the whole piece seems to be the small hand-scratched number on its own, then the fraction numbers are the other two glazes that have been put one on top of the other over the base glaze randomly.
Each number would relate to a specific glaze recipe.
The results can then be repeated again, using the numbered glazes in the same order.
They would have had so much fun, trying different glazes under and over each other!
Their success with those experiments is an amazing rainbow of colours that are outstanding even today!
Hope that helps ......

How lucky of you to have a dated piece, as there is no need to guess when it was made
Yes they did have shape numbers in those early days and these were impressed on the base, though not always ....!

I would like to spend time researching the glazes that they used .... one day!

Thanks so much both of you. The numbered vase is not mine, it was in the antique shop, but it intrigued me. Maybe it will be mine one day perhaps, after I've saved up for it!