Question about CMA but more in particular- Adjustments

[Harvey Gill]

Hello I just finished the book on Rental Property investing by Brandon Turner. I've been watching a ton of videos on CMA's and I've been practicing as well and hopefully I will get a rental soon!

One question that has me a bit confused still - so for adjustments, where can I go to find these or how can I calculate these? For example if my comparable has one more bedroom, how can I calculate to find out how much 1 more bedroom would cost? 

Side question- do you guys recommend manually doing CMA's or using an online CMA service?

Thanks!

-Harvey