In the main menu bar: Window > Animation Editors > Blend Shape
In scene view: Panels > Panel > Blend Shape
Each slider provides a way for you to set the target weight quickly. By default, each target slider sets values from the minimum value (by default, 0.000) to the maximum value (by default, 1.000). The current weight is displayed in the target weight box below the target slider.
You can change the orientation of the sliders. For more information, see Edit blend shape deformers.
Each box displays the current weight for each target. By default, a target weight can range from the minimum value (by default, 0.000) to the maximum value (by default, 1.000). As you change values, the target weight sliders update according to the value you enter in the target weight boxes.
You can enter positive and negative weight values to invert or amplify the target’s influence. If you enter a value greater than the current maximum value (by default, 1.000), the maximum value changes to double the value or to 10.000 if double the value is greater than 10.000. If you enter a value less than the current minimum value (by default, 0.000), the minimum value changes to double the value or to -10.000 if double the value is less than -10.000. When you enter values less than the current minimum or greater than the current maximum, the target weight sliders change to reflect the new range of values.
By default, the target name is the name of a target object (for example, nurbsSphere1). If you prefer, enter some other name for the target name. Entering a new target name does not change the name of the target object. Changing the target name is useful if you want to give a more appropriate target name after you’ve created the blend shape deformer.