Can you explain how Angle measurement "Pointing Error" works?

Total Stations

A rudimentary example of error accumulation of a total station in an angle and a distance is$,$

Angular $-$ Distance Error.

Instrument is a Topcon $603$ @ $1$ Sigma or $68\%$

DIN $18723$ is measuring the angle $1$ direct and then $1$ reversed pointing.

Angular Measurement:

Standard Deviation is $3^{\text{'}\text{'}}$ based on DIN $18723.$

Distance Measurement

Measurement accuracy is $+-(2mm+2ppm)$

Instrument ${?}^1$ set at $2,$ turn $1$ direct & $1$ reverse, mean $=145$

Backsight at $1,$ distance ${850\mathrm{.}00}^{\text{'}}=D_1$ Foresight at $3,$ distance ${1250\mathrm{.}00}^{\text{'}}=D_2$

Angular Measurement

Pointing Error

${}_p=$ Estimated standard deviation as $2^{\text{'}\text{'}}$

$n=$ Number of pointings

${}_{PE}=(\frac{{}_P}{\sqrt[\phantom{2}]{n}}),{}_{PE}=(\frac{2^{\text{'}\text{'}}}{\sqrt[\phantom{2}]{2}})=+-{1\mathrm{.}41}^{\text{'}\text{'}}$