What kind of accuracy can one expect from older Starrett tools?

If the oldie is in good condition, not abused, and the contact edges are square then it will be just as accurate as a modern equivalent. Actually, my vernier calipers are old and have that fine adjust feature. It is more accurate than my more modern dial calipers. The only problem is that it requires magnification to read it accurately now that my eyes are older.
 
Accuracy would be fine, as mikey said, but I would hold out for the later model with a 50 division vernier rather than the 25 division, they are much easier to read, and have both inside and outside measurements on the same side of the instrument, plus, they have a center to center feather for setting dividers and trammel points.
 
The old Starrett tools were made at least as accurate as the new ones, perhaps better than some of their latest products. Still, wear can take its toll, especially on tools that are not hardened, Starrett tools were usually properly hardened in the old days.
 
Tools are only as accurate as you can verify, for this you will need gauge blocks.
Measure a stack then measure the part, if they measure the same you are within the gauge blocks accuracy range.

Gauge blocks are available in different grades, use a grade that your level of accuracy requires.
The closer the tolerance the higher the price.
Choose wisely.

https://westportcorp.com/collections/mitutoyo-square-gage-block-set-inch
 
Back in the 1980's I purchased (yard sale) a boxed No. 122 36" Starret Vernier Caliper. (25 div vernier) The box had stamped on it, USAAF (Us Arrmy Air Force) dating it to during or before WWII. I took it to work, had it certified, (no problem, just difficutl reading the vernier) and used it until I retired, 15 years later. It passed certification every six months.
 
I love all of my Starrett tools, some of which go back decades before me i.e. ancient.
They are all in top condition almost like new. The one in the picture looks to me to be sort of haggard especially when I blow the image up. I’m no expert, but I would steer clear of it.
The jaws look to be somewhat worn and the scale is difficult to read.
But that’s just this old mans oppinion.
 
I used to swear by my 6" vernier calipers, they had a custom pocket on my apron and I used them all the time. Now I have trouble reading my dial calipers without glasses. Plan ahead, your vision won't always be 20/20.
 
I have the same model, picked up at a hamfest for $20. Starrett is a well known brand and made quality metrology tools, especially when that one was made. Aside from damage due to wear or misuse, there is little that can go wrong with one of these.

The jaws should be parallel, as determined by closing the cleaned jaws and holding to the light. You shouldn't see any light coming through the jaws. Another way to check that were were taught in metrology training was to gently grab a gage block in the jaws and hold it with the jaws horizontal. If the gage block rotates, the jaws aren't parallel and the tight spot is the point of rotation.

The vernier should be properly zeroed when the jaws are closed. As to proper calibration with a set of gage blocks, I wouldn't worry about that. I haven't seen a set of gage blocks that can calibrate the full range of a 24" caliper anyway. People seem to forget that this is a hobby machinist site.

To check calibration, I would use some 1-2-3 blocks, verified with a micrometer. A stack of two will give you calibration points at one inch intervals up to six inches. If you're good at those points, you should be good the rest of the way. Alternatively. you could mike a six inch parallel and measure that.

If you are in a production situation and require ISO9000 certification, you are most likely having a certified metrology lab do your calibration anyway. Otherwise who's going to argue with you if you say a chunk of steel is 22.364" long?
 
Accuracy aside, that fine adjust feature allows the caliper to square up on a part better than a thumb wheel does. When it is square on the part, you will know it. I suspect that is one reason why these old style calipers were so accurate. These things are no longer in vogue and go for stupid cheap prices. Wait for one in mint condition. I recommend a Mitutoyo or Helios as well.
 
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