A circuit tester can be purchased at your local hardware store, for example Ace, Home Depot, and Lowe's. If you want to shop for it online, the circuit tester can be bought on the stores' websites along with sites like Amazon and eBay.
One can purchase a robin loop tester from Ebay. One can also purchase a robin loop tester from electrical shops or from electrical dealers which carry robin loop testers.
A pH tester is used to determine the acidity or alkalinity of a substance. One can purchase a pH tester online at websites including Home Depot, Amazon and Sears.
One could purchase a portable hardness tester at MCS Direct, and on Amazon. Another place to purchase a portable hardness tester online would be Martrow which offers free shipping in the United States.
Christmas light testers are very easy to purchase online. One might find a reasonably priced tester at Amazon, Overstock, Walmart, or at any other specialty store.
it works
by sending electricity through them
That would depend on the speed tester you were looking to purchase. In general speed tests refer to internet speed tests which can be found for free at the Speedtest website.
If someone is looking to purchase a diesel engine compression tester there are a variety of online sources. One can find these testers on sites such as Mercedes Source, Harbor Freight, Amazon or eBay.
One can purchase a gold tester from the Jewelry Tools website, which sells a high quality and well rated tester. The tester is currently being sold for about one hundred and ninety dollars.
A LAN tester is a circuit used to check the LAN cables. They run for approximately $41.00 in most electronic stores.
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You can purchase a battery tester at most big name stores, like Walmart, Meijer, or any hardware stores like Home depot, or Ace Hardware. Sometimes you can find them cheaper at yard sales.