A clockmaker in Kyoto builds a pendulum clock…

Step 1. The relative error in $L$. $\dfrac{dL}{L} = \dfrac{0.002}{0.994} = 0.002012$.

Step 2. The relative error in $T$. Since $T \propto \sqrt{L}$, we have $\dfrac{dT}{T} = \dfrac{1}{2}\,\dfrac{dL}{L} = 0.001006$. The percentage error is $0.1006\%$.

Step 3. The period. $T = 2\pi\sqrt{\dfrac{0.994}{9.81}} = 2.0000\ \text{s}$. Then $dT = 0.001006 \times 2.0000 = 0.0020\ \text{s}$.

Step 4. One day. $0.001006 \times 86400 = 86.9\ \text{s}$. The clock would be out by about $87\ \text{s}$ every day.

Gain or loss. A longer pendulum has a longer period, so each swing takes more time than the clock expects. The clock loses time.