$\left( {\frac{{\Delta T}}{t}\, \times \,100} \right)\,\% \, = \pm \left[ {\frac{1}{2} \times \frac{{\Delta {l}}}{{l}}\, \times \,100 + \,\frac{1}{{2\,}} \times \,\frac{{\Delta g}}{g}\, \times \,100} \right]$
$ = \,\,\, \pm \left[ {1\,\% \, + \,2\,\% } \right]\,$
$\therefore \,\,\,T\,\, = \,\, \pm \,\,3\,\,\% $