Ahmed should use a scale or a weighing machine to measure the weight of an object.

Instrument to Measure Weight

• A scale (often called a weighing machine) is specifically designed to measure the weight, which is the force exerted by gravity on an object.
• Examples include spring scales and digital scales, which give readings of weight by measuring the gravitational pull on the object's mass.
• The reading on a scale reflects weight, usually displayed in units like newtons or kilograms-force, depending on calibration.
• To measure weight accurately, the object is placed or suspended on the scale, and the scale provides the measurement by balancing or sensing the force.

Thus, for Ahmed's purpose, a weighing scale or weighing machine is the correct instrument to use. It directly measures weight, unlike balances which typically measure mass.