why are adjustable pipettes better at measuring small volumes and glass pipetted better at measuring bigger volumes

Trick question?
From Analytical Chemistry Handbook by
John A Dean.

ASTM E969 Class A transfer pipet @ 0.5 ml
has a tolerance of +/- .006 ml.
class B +/- 0.012 ml
(note significant figures)
Serological pipet ,class B .05 ml tolerance of +/- 0.01 ml

For apples to apples
A Serological pipet of 0.1 is at +/- 0.005ml or 0.5%
For an Eppendorf micro pipet 1000 micro liters
has a similar 0.5% tolerance..

From the practical side the adjustable pipets are simply easier to use. The process is simpler. As the volume increases air leaks on the piston etc mount up and large volumes are more difficult to control. A 100 Ml Tranfer pipet may take a couple squeezes of the bulb to get it to fill and a couple slips of the finger to get the volume correct.


An Eppendorf micro pipet