Instruments for Measuring a Difference in Level
Three sighting levels and a water-trough level, to find how much higher one place stands than another.
The sheet figures three instruments for measuring a difference in level, labelled M n, a S t y, and r f. A screw-adjusted variant is explained: sighting so the eye a and the two marks S t align with a black strip on card r, one drives a nail at f in a graduated staff, repeats at the opposite place with eye y, and the distance between the two nails M and n gives how much lower one place is than the other. A third note tells how the level itself should be made, a fir bar two braccia long with a finger-wide water channel, a wetted cord, and two iron sights set at m n. Later Spanish annotations in a different hand also appear at the top of the page but are not transcribed here.
On this page
Three instruments to measure a difference of level
Three leveling instruments are drawn and labelled M n, a S t y, and r f, forming a set for gauging how much one plane rises above another.
Screw-adjusted level and how to use it (a, S t, r, f, M, n)
Set the level between eye and target, raise a graduated staff until the eye a and sights S t line up with the top of the black strip on card r, and mark it with a nail at f. Repeat at the opposite place using eye y; the first nail is M, the second n, and the span M-n is how much lower one place lies than the other.
How the water-trough level is made (m m, cord)
The level should be two braccia long, an inch square, and of fir so it will not warp, with a finger-wide, finger-deep channel on top. Wet the cord and fill the channel until the water stands even with the banks, clear the overflow with the fingers, then set two cord-thick irons at m n so one meets the other for sighting.