(e) "Commercial purposes" include the determination of the weight, measure, or count of any commodity or thing which is sold on the basis of weight, measure, or count; or the determination of the weight, measure, or count of any commodity or thing upon which determination a charge for service is based. Devices used in a determination upon which a charge for service is based include, but are not limited to, taximeters, odometers, timing devices, parcel scales, shipping scales, and scales used in the payment of agricultural workers.
"Commercial purposes" do not include the determination of the weight, measure, or count of any commodity or thing which is performed within a plant or business as a part of the manufacturing, processing, or preparing for market of that commodity or thing, or the determination of charges for the transmission of letters or parcels of less than 150 pounds, except when that determination is made in the presence of the customer charged for the service.