Private method naming convention

Question

Is there a convention for naming the private method that I have called "_Add" here? I am not a fan of the leading underscore but it is what one of my teammates suggests.

public Vector Add(Vector vector) {
    // check vector for null, and compare Length to vector.Length
    return _Add(vector);
}

public static Vector Add(Vector vector1, Vector vector2) {
    // check parameters for null, and compare Lengths
    Vector returnVector = vector1.Clone()
    return returnVector._Add(vector2);
}

private Vector _Add(Vector vector) {
    for (int index = 0; index < Length; index++) {
        this[index] += vector[index];
    }
    return this;
}

Answer 1

I usually see and use either "AddCore" or "InnerAdd"