In order to work with quantitative sections of the study material, it is important that you be able to work with a financial calculator. The exam questions are construction with the assumption that the candidates have the ability to work with a financial calculator. CFA Institute allows two types of calculators in the exam:
The Texas Instruments BA II Plus (including the BA II Plus Professional) 
The Hewlett Packard 12C (including the HP 12C Platinum.)
Only these two calculator models are approved for the CFA exam. You must carry the calculator with you to the exam room as the calculators will not be provided to you there.
Stay away from tampering with the calculator or writing anything on it as every student’s calculator will be inspected prior to the exam.
You must practice the use of calculator and will benefit tremendously if you know how to perform all the required calculations such as bond calculations on the calculator you carry. You are not allowed to carry the instruction manual with you to the exam room. You may however carry calculator covers, key stroke cards, and loose batteries to the exam room.
Calculator Guides
BA II Plus Guidebook available here.
HP 12C guidebook available here.