The uniforms don't get credited back 100%. The E-3 pay accrues from the first day, but isn't paid in RTC. The difference gets made up afterwards. The salary is also prorated. So If you ship on the 12th of the month, you'll only get a month's pay minus 11 days. Sort of. The part that's hard to understand is what a month's pay is. Since military guys are salary, a month's pay is 1/12th of a year's pay. It seems simple enough, but it isn't. Payday is half of a twelfth of a year's pay. So, figure the "monthly" pay rate, multiply that by 12, divide by 365. This is your "daily norm". Multiply the "daily norm" by 365, divide by 24 and you arrive at what your next two paychecks are going to be. UNLESS somebody recalculates the daily norm in between.
I thought that being a nuke was complicated until I spent my last month of active duty in the New London disbursing office. Go ahead ask me about travel claims.
My brain hurts now.