In the settings for scaled watermark, the explanation text reads: “Enter a number ranging from 0 to 100. 100 makes width of watermark image equal to width of the image it is applied to.”
But there is no input option to enter a number. The input option is a slider which doesn’t show how much percent you have set it to. You would have to look into the source code (after you save it) to see the input value.
I would recommend :
a) having a freeform option
b) show the percentage of the slider