From what I understand about setting the regulator and the hammer spring —
without a chrono it's like trying to find Nemo — in the dark, without flashlight, nightvision, or thermo....
Personally, I'd order the chrono today....
I've learned a lot from
Bob Sterne. He's writing a lot of good articles over at
HardAir Magazine. One is on
how to tune a regulated PCP (though if you're new to this tuning game, you'll probably benefit from reading some of the other articles to really understand what you're doing. I know I have!

).
LINK: https://hardairmagazine.com/author/bob-sterne/ Matthias
Some of Bob's article titles: ▪PCP Efficiency - What Is It? What Changes It?
▪How to Obtain Maximum Power from PCPs
▪Using Hammer Strike to Control PCP Power
▪Conserving Air In PCPs — Hammer Bounce and the SSG
▪Airgun Pellet Penetration – The Real Story
▪The External Ballistics Of Slugs In Airguns