If one wishes to duplicate or emulate this seemingly English or perhaps originally Dutch method of measuring powder for your firelock, fine.
If you wish to have more accurate stricken measures, you will reduce the diameter of the hole in the powder measure to no more than about 3/8", as in a ctg. brass or brass tube, or commercial measure no larger than that. This size makes duplicating accurate measures of powder, much easier. The smaller the diameter of the measure, the closer will be subsequent charges.
I've found pouring from a horn with a 1/4" hole, into a measure no more than .375", and as small as 1/4", that my thrown charges rarely vary more than 1/2gr. weight. Consistency is important in all of this.
The larger the diameter of the hole in the measure, the greater the opportunity for not filling it exactly the same, each time. For smaller bore guns, this can be very important for consistency. The larger bores usually give more leeway on this. I use a 1/2" diameter measure for the .69 - it seems not to care a whole lot, unlike the .32, .40 and .45. Lucky for them, the measure is usually smaller to make it easier to pour into a smaller bore.