Shares in Caterpillar (CAT -3.07%) were down by 3% in today's trading at 3:20 p.m. ET. The decline comes on a bad day for the markets overall and, more importantly, for the commodities that drive orders for its machinery.Caterpillar's end marketsCaterpillar is well known for its construction equipment and its sales aligning with the construction cycle. And it plays a significant role in mining machinery, gas turbines, generators, solar gas turbines/compressors, and energy storage, with some construction mac ...