A draft shield is required for analytical balances. Common draft shields are either removable glass shells or glass doors. The shield prevents air currents from causing the balance pan to move, which results in fluctuating readings. By protecting the balance pan with a draft shield, a single, constant mass reading can be observed. Some balances have an indicator light to indicate when the balance has stabilized. The balance shown indicates that the mass reading is constant when a "g" lights up to the right of the numerical reading.