The HP-41C analog on my phone gives the right answer. " data-large-file="https://hackaday.com/wp-content/uploads/2026/05/41c.png?w=278" src="https://hackaday.com/wp-content/uploads/2026/05/41c.png?w=178" alt="" width="178" height="400" srcset="https://hackaday.com/wp-content/uploads/2026/05/41c.png 864w, https://hackaday.com/wp-content/uploads/2026/05/41c.png?resize=111,250 111w, https://hackaday.com/wp-content/uploads/2026/05/41c.png?resize=178,400 178w, https://hackaday.com/wp-content/uploads/2026/05/41c.png?resize=278,625 278w, https://hackaday.com/wp-content/uploads/2026/05/41c.png?resize=684,1536 684w" sizes="(max-width: 178px) 100vw, 178px"> The HP-41C analog on my phone gives the right answer. Three resistors in parallel: 4.7 k,Ω 22 kΩ, and 3.3 kΩ. Quick! What’s the equivalent value? You can estimate it, of course, but if you want the actual 1.8 kΩ (approximately) answer, you probably reached for some kind of calculating aid.…