function _addGrace(minmax, grace, beginAtZero) {
    const { min , max  } = minmax;
    const change = toDimension(grace, (max - min) / 2);
    const keepZero = (value, add)=>beginAtZero && value === 0 ? 0 : value + add;
    return {
        min: keepZero(min, -Math.abs(change)),
        max: keepZero(max, change)
    };
}
@param minmax
@param grace
@param beginAtZero
@private