Welcome, and thanks for asking our advice
There is some debate on the safety of relying on the disk cavity number to determine how much powder you are putting into your cartridges.
To say the number is not relevant is incorrect. To say the number is wrong might be more correct. To say the number is just a guide as to what to expect your powder to weigh when you DO drop it into a scale is more correct.
It is possible to use the Lee dippers or the Auto-Disk to load without having access to a scale, but it is inadvisable. If you use this practice, I HIGHLY recommend staying in the mid-range of loading. For Cowboy Action Shooting power levels, you should be quite safe, but if you post what powder and bullet you are using, what load manual you got your recipe from and what cartridge (38-44? 45 Colt? 44-40? 38 Special?) we could probably help you more.
And GET A SCALE as soon as you possibly can. The Lee Safety Scale is only about $30 (and a lot less used at guns shows and swap meets) and as accurate as any powder scale commonly used (+ or - 0.1 grain). It is tricky to use and some don't like it, but if you read the instructions, you will do fine.
I didn't like mine at all until I got a copy of the instructions and now find it usable. Prefer my RCBS 10-10 though.
Good Luck, I lood forward to helping as soon as I know 1) The Cartridge 2) the firearm, 3) the powder 4) the reference you got your recipe from and 5) the bullet you intend to shoot.