The unit of percentage error is

The outer and inner radii of a hollow cylinder are $(4.23 \pm 0.01) \text{ cm}$ and $(3.89 \pm 0.01) \text{ cm}$ respectively. What is the thickness of the wall of the cylinder?

Two resistors of resistances $R_1 = (100 \pm 3) \,\Omega$ and $R_2 = (200 \pm 4) \,\Omega$ are connected in series. The maximum absolute error and percentage error in the equivalent resistance of the series combination are:

The resistance $R = \frac{V}{I}$ where $V = (200 \pm 5) \ V$ and $I = (20 \pm 0.2) \ A$. The percentage error in the measurement of $R$ is: (in $\%$)

$A$ person measures the depth of a well by measuring the time interval between dropping a stone and receiving the sound of impact with the bottom of the well. The error in his measurement of time is $\delta T = 0.01 \ s$ and he measures the depth of the well to be $L = 20 \ m$. Take the acceleration due to gravity $g = 10 \ ms^{-2}$ and the velocity of sound $v = 300 \ ms^{-1}$. Then the fractional error in the measurement,$\delta L / L$,is closest to: (in $\%$)

Zero error belongs to the category of