If there is a single tool that is easily pressing for every Heating plus Air Conditioning professional to own it is a multimeter, a multimeter is a special tool that fits in the palm of your hand. A multimeter usually has a numerical display plus a graph to measure all of the values. Digital multimeters are low-cost plus they can be bought at any hardware store. A multimeter can measure voltage, current, plus also resistance. I bought a new multimeter a couple of weeks ago plus I used the machine every single day on the job, however last week, I was laboring on an Heating plus Air Conditioning installation job plus I was using the multimeter. I turned it on but I did not get any power at all. I hit the side of the machine, however it still did not power on. I put a couple of new batteries in the back of the digital machine however that did not work either. I use that tool every day for weeks plus weeks plus I could not assume that it suddenly stopped laboring separate from a single problem. I had to go to the shop plus borrow another tool so I could finish the Heating plus Air Conditioning installation job. It took an hour to drive back to the shop plus then back to the residence. I spent numerous hours laboring on that Heating plus Air Conditioning installation job plus I did not have our favorite tool to get everything done. I took the multimeter back to the hardware store as soon as our work day was done. The guy exchanged the machine separate from asking a lot of questions, so it might have been a manufacturer defect.