Doubts in advance tax calculation

Small query regarding Advance tax calculation and Penalty calculation.

Question 1:
Let us assume that Mr. X earns a variable salary each month as it depends upon the fluctuation of the currency conversion rate from USD.  So in this case, how a person should calculate Advance tax payment on each due (15/9, 15/12, 15/3)?

For example: if he has salary like this, is it the following computation correct?
April - 0
May - 0
June - 45,000
July - 50,000
August - 60,000
September - 55,000
    - Now in this month before 15th, How much he has to pay as Advance tax without knowing how much he's going to earn in future to calculate the Total taxable income (ignoring all tax exemption and deductions) at the FY end to pay 30% of that now??
    
October - 70,000
November - 50,000
December - 0
    - Similarly, at this stage how much it should be?
January - 0
February - 45,000
March - 50,000
    - Similarly, at this stage how much it should be?

Question 2:
If Mr. X missed to pay all these advance tax, how to calculate the total amount with penalty now and furnishing this detail in his ITR?

For example, his total income is 7,00,000 and has tax exemption and no deduction.

Thanks