2 56 Mr. Babbage on a method of expressing 
adjustments, this space may be subdivided into three, and 
appropriated to each of the three species just enumerated, the 
permanent, the usual, and the periodic : if their number is 
small, it is better merely to distinguish them by a modifica- 
tion of their signs. It is sometimes impossible to perform 
such adjustment, except in a particular succession ; and it is 
always convenient to adhere to one particular order. Num- 
bers attached to their respective lines denote the order in 
which the parts are to be adjusted ; and as it will sometimes 
happen that two or more adjustments must be made at the 
same time, in that case the same numbers must be written on 
the lines belonging to all those parts which it is necessary to 
adjust simultaneously. 
If it is convenient to distinguish between the species of 
adjustments without separating them by lines, this may be 
accomplished by putting a line above or below the figures, 
or inclosing them in a circle, or by some similar mode. I 
have attached the letter P to those which are periodic. 
It would add to the knowlege thus conveyed, if the sign 
indicating adjustment also gave us some information respect- 
ing its nature ; there are, however, so many different species, 
that it is perhaps better in the first instance to confine our- 
selves to a few of the most common, and to leave to those 
whom may have occasion to employ this kind of notation, 
the contrivance of signs, fitted for their more immediate 
purpose. 
One of the most common adjustments is that of deter- 
mining the distance between two parts, as between the point 
of suspension and the centre of oscillation of a pendulum. 
This might be indicated by a small line crossing the vertical 
