The loth measurement system was used in the Middle Ages, in European countries such as modern Austria and Germany, luoti in Finland and lõdig in Norway.
Copper was used as an alloying metal in silver alloys.
Like the metric standard, the loth standard was an indicator of the quality of a silver item.
The loth mark of silver shows the content of precious metal in the alloy - the number of loths in one Cologne mark of the alloy. 1 Cologne mark was equal to 233.855 grams, while 1 loth was equal to 14.616 grams. Thus, the loth was equal to 1⁄16th of a stamp, that is, the weight of the loth depended on the weight (mass) of the stamp.
For reference: in Medieval Europe, the mark was originally used as a unit of measurement for the weight of silver and gold.
And only after that it began to be used as a monetary unit. Due to the fact that the weight characteristics of brands differ, hence the inconvenience of this measurement system. 
13 loth silver mark
A figural or alphabetic symbol (in some cases accompanied by a number) identified the town control office.
Silver fineness was indicated in "loth" until 1867 in Austrian empire and until 1888 in German empire:
12 loth silver= 750/1000
13 loth silver= 813/1000
14 loth silver= 875/1000
15 loth silver= 937/1000.
Loth standard in carats:
6 loth – 9 carats
8 loth – 12 carats
10 loth – 15 carats
12 loth – 18 carats
14 loth – 21 carats
16 loth – 24 carats