Complex sentence: Proposition 13 limited taxation based on the assessed value of real estate to 1% per year; however, the parcel tax is a flat tax on each parcel of real estate, and does not vary according to the value of the property.
Split into simpler sentences: Proposition 13 limited the property tax rate based on the assessed value of real estate to 1% per year. However, the parcel tax is a flat tax on each parcel of real estate, and does "not" vary according to the assessed value of the property.