A few months ago I posted about how I had some chundoo shafts purchased about 20 yrs ago, had weighed and sealed them back then, but didn't remember what spine they were supposed to be. I took the three closest in weight and made up 28" arrows with 125gr tips to try.
I am shooting a 47# recurve at 26" draw with ff string and 2016s 28.5" with 145gr tips shoot bullet holes in paper so had an idea of where I should be - but not what I had. One shot just like the 2016s but the other two were hitting nock right (I shoot left) at my 5yd form butt.
I have since built a simple spine tester using a dial caliper to measure deflection. The one that shot ok measured 57# and the other two were 49# and 45#. I cut an inch off the 49# and it flew much better as did another at 48# also cut to 27". For reference I measured a 2016 across 26" and then found an old post here of what it should be at 26" and was within .005" which verified the tester and my technique.
I have six more shafts in two weight groups that measured 51# to 54#. May make a few flu flus to try. When it's time to get a matched set it's looking like I will be able to go with 50-55 at 27" or 55-60 at 28". Still got time to decide on wood type and overall weight. Boy, it's fun playing with woodies.