@Rider_X - Fitted the new chain and did my first measurement. Must be doing something wrong

but my gear's not accuirate enough. 6 links of old chain was 15.26mm

6 links of new chain is 15.22mm

my caliper is not long enough to measure more than 6 or 7 links

@Criggie how are you measuring the chain? It can be hard to measure off the bike. I actually take the same approach as a cc-2 too outerlink roller to inner link roller. I use calipers that measure to 1/1000 inch and I have had much more accurate results than using park tool. It took a bit of practice as at first I was some times measuring against the outer plate instead of the roller. I still measure in triplicate: three points on the chain.

@rider_x I have the chain on the bike and have the pointy bit of the vernier hard against the edge of one side plate. The other end is pointed the opposite way and I have visually adjusted the point to be dead on the edge of the sixth outer plate following.

@rider_x so its not ideal. I suppose I could measure 6 and a half plates - would that be adequate ?

actually that should work fine knowing its 13 half links

@Criggie Visually lining up the measurement can be difficult, this is why I measure the inter-roller width as I can physically push the caliper against both measurement points. I then lock the caliper and take the reading. Measuring the inter-plate difference may be more difficult as you can only push against one plate at a time. I also measure in triplicate at three different places along the chain and take an average.

@Criggie Measuring the inter-plate distance will capture physical elongation, but will not capture other factors affecting chain pitch (as seen by a cog or chain ring), such as roller wear, and inner-plate wear (the inner plate now acts as a bushing in modern chains). An inter-roller measurement will capture the roller wear and the wear on one of the inner-plate rollers. This is of course not perfect, but all we need is a measure that is repeatable and changes consistently with chain wear.

@Criggie - As a aside, I suspect the answer to my chain wear question may be measurement scale, as the CC-2 provides a "%" scale, that does not map linearly to the chain length (as one might expected), while the other figure showed chain wear as a actual chain length. I should take the time and map out the CC-2 % scale to show this.