C

To calculate the weight measured on the spring balance when a person is in a descending lift with uniform acceleration, we need to consider the effective weight of the person during acceleration.

1. **Given Data**:
- Mass of the person (m) = 60 kg
- Acceleration of lift (a) = 1.8 m/s²
- Acceleration due to gravity (g) = 10 m/s²

2. **Weight Calculation**:
The effective weight (W') can be calculated using the formula:
$$ W' = m(g - a) $$
where:
- W' is the effective weight
- m is the mass
- g is the acceleration due to gravity
- a is the downward acceleration of the lift.

3. **Substituting Values**:
$$ W' = 60 imes (10 - 1.8) $$
$$ W' = 60 imes 8.2 $$
$$ W' = 492 ext{ N} $$
Therefore, the weight of the person as measured by the spring balance will be **492 N**.