To measure 10.5g of rock salt, you can use a digital kitchen scale. A digital kitchen scale is a precise instrument used to measure the weight of ingredients, especially in cooking and baking. Here are the steps on how to use a digital kitchen scale:

1. Place the scale on a flat and stable surface.

2. Turn on the scale and select the unit of measurement (grams).

3. Place an empty container or bowl on the scale platform.

4. Press the "tare" or "zero" button to reset the scale to zero. This eliminates the weight of the container.

5. Gradually add rock salt to the container until the scale displays a reading of 10.5 grams.

6. Once you reach 10.5 grams, stop adding salt.

7. Use a spoon or scoop to transfer the measured salt to your desired container.

Ensure you add rock salt slowly and carefully, especially when approaching the desired weight, to achieve precise measurement. Digital kitchen scales are widely available in kitchenware stores and online. They come in different sizes and with varying capacities. Choose one that suits your measurement needs and kitchen space.