http://www.cpsproducts.com/site/ProductsHTML/ChargingScales.html

http://www.allied-refrig.com/14%20Refrigerant%20Charging,%20Recovery%20&%20Supplies.pdf

http://www.vtechonline.com/

http://www.air-conditioner-selection.com/how-to-recharge-air-conditioner.html

http://www.inficonrefrigerantchargingscales.com/

http://www.ecicomplete.com/vacucharge.html

http://www.hcrefrigerant.com/charging.htm

http://chargetech.net/

http://www.licensedelectrician.com/Store/Charging_Scales.htm

http://www.kramerusa.net/misc/tech_tips/REFRIG_CHARGING_GUIDELINES.pdf