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All the changes you make are reflected in 2 places - Calculation Lines and Payment Calendar. For more information about general contract changes see attached video:
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https://www.youtube.com/watch?v=LPYMrWzxQNM&list=PLGrwYyCxmp1RjVv_gk7TzUZpOnhoOUDot&index=19
In this case, we are choosing the process of changing Principal Amount, which is described below:
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Note:
After realizing changes, it's necessary to update calculation through button called Calculation, which is situated in section Process. All of the changes you made will be reflected in the Calculator Lines and Payments Calendar.
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Follow up:
How to change financing period