Antique  folding sovereign scales by De Grave and Son, St Martin's-Le-Grand, London. The business was known as De Grave and Son from 1817 to 1844.  
The scales are housed in a mahogany case which measures  14cm l x 2.8cm w  x 1.8cm d.
The scales fold out to operate and the instructions for use are printed in the inside lid and base of the scales and read:
'These balance[s] are as accurate as the best of scales;
more expeditious, portable, and not so liable to be out of
order. they may be tried with sealed weights at any time fir the satisfaction of those who refuse to take money by them.Before you shut the box put the slide to the cipher and turn up the scale.
Sovereign ....... 5dwt*[. 2 1/2 gr.]
Half-Sovereign .. 2[dwt 1]3 [1/8 gr.]
The turn at the end for a Sovereign:-to the centre
for Half-a-Sovereign, and the slide at the cipher, where
it stops.In removing the slide from the cipher towards the figure 12 each degree indicates a penny.