Left: You will find such a too pan scale nearly in each science lab of German schools. The photo shows how the metal cap of one Liquemin bottle is balanced by a square of aluminium foil usual in the trade. Its size result either by calculation or by weighing on a sophisticated scale: 81 x 81 mm of the foil weigh 200 mg, that means a piece of 6 x 6 mm is 1 milligram (mg).
Such a tiny piece of foil causes a significant reaction of the scale, so its sensibility is 1 mg.
Middle: The balancemaker Said Mohamed El-Tobgi*) on this photo manufactures similar scales in the suq of Cairo. Their sensibility is less than 0.1 g (half a Liquemin metal cap), the latest model has a sensibility of 10 mg.
Right: You can make your own "postcard scale" using a description an taking 1-Yen coins as 1-gram weights.
There are many other dead easy methods to make ones own scale.
*) Address: Said Mohamed El-Tobgi  7 Souk El Ferak (Jewish Quarter) Sagha Building Hag Mohamed El Shataf)