No gauge needed, use a tape measure. The standard link length is 1/2 inch. Line up a pin with the 1 inch line (more accurate than the zero end of the tape). Look at the 8, 8 1/2 or 9 inch mark to see if the associated chain pin also lines up. If the pin is more than 1/8 inch from the tape line where it should be, replace the chain.
And I... well, I slacked off in May. Monthly miles are 120 and a few tenths.
Good ride this morning however. I felt good (after a week off...). I was surprised to see that the speedo was reading 28 mph a stretch where I usually barely make 22.
I had a better ride on Friday: 31.9 km/h average speed (20 MPH) and felt like I had a lot more there. I hope to hit over 34 km/h on this 26 km ride this year sometime. It should be possible......
My bike speedometer is one of these self-stopping and starting ones so if (more like, WHEN) I hit stoplights, the average speed and elapsed time suffers a bit more than it did when I had the manually operated one a couple of years back.