As the only female student in my college engineering class, I excelled on the concept of differentials, so much that I ruined the grade curve for the class – or so my classmates insisted.

One night at dinner, my dad, the manager of manufacturing engineering for the old Grumman Aviation in Bethpage, L.I., was discussing a serious design flaw in a certain new aircraft.

“Sounds like an aerodynamic wing differential problem to me,” I said. Bingo! His eyes lit up. Several weeks later, the engineers solved the problem.

As the money manager in our family, I have come to realize that tiny differentials in interest rates and penalties ultimately make a huge difference in saving for retirement.

Over the years, I have learned that I must ask as many questions of the people who run banks, credit-card companies, investment firms, insurance companies and, yes, Social Security, as I did back in engineering class at Hofstra. What I have learned is that the differential is probably not going in your direction.

As an artist, teacher and grandmother, I’d rather be filling those roles. Instead, I have a full-time career inspecting the differentials at the ever-shifting companies that are only too glad to handle our money. I realized this a few years ago when I investigated the protection of our retirement accounts by the Federal Deposit Insurance Corporation. While we are hardly wealthy, if you live long enough and are lucky you may actually accumulate IRA and Keogh accounts that reach the $100,000 level.

These days I pay much more attention to business news than I used to. Somewhere, I heard something about FDIC insurance on retirement accounts that triggered off concern about our accounts. However, when I asked officials at our local bank, I was told it was not worth worrying about, since I maintained separate accounts under $100,000 and each was separately insured.

I was skeptical and called the FDIC directly. After working my way up through the normal maze of telephone-answerers, I managed to reach an official who sounded as if she knew what she was talking about. I was horrified to learn that each bank is insured for $100,000 for all combined retirement accounts similar to ours. Bingo!

Armed with my information from the FDIC, I went back to both our banks, where managers admitted they had not known this.

One manager, a bright guy, spent a lot of time calling experts in his home office to verify. He then delegated a couple of his clerks to facilitate our withdrawal of the excess over $100,000. From what I have learned, companies can accept your money, but giving it back is laborious. It took an hour but he got it done.

The official at the next bank was able to deposit our excess funds – after he checked the wrong boxes the first time, that is.

Because we are not comfortable with major investments and speculation, we accept that keeping our money in the bank at low interest rates is the price for safety. However, paying a $50 administrative fee for each account – paying for bad information, that is – only adds insult to injury.

Then there was the investment company, chosen by one of our employers, which handled our modest annual donation of stock to a childcare agency. There was a slight problem: the clerk at the investment company mistakenly gave away our entire portfolio, worth 40 times our donation. Fortunately, an auditor at the child-care agency noted the huge discrepancy, made a call, and we were able to get it straightened out. I haven’t figured out whether the children lost money in the differential on the stock market over those few days.

Next came Social Security. We hardly want the federal government turning over this hallowed national social umbrella to the assorted incompetents out there who’d love to handle our money. However, it did take me two full visits (standing in line, during the ‘flu season) to the district office to get the spigot turned on. Somebody had forgotten to file our request the first time. We did get our first payment, retroactively. I checked. You have to check the differential every time.

Ms. Vecsey, an artist, has made 13 trips to a child-care agency in Pune, India. She lives in Port Washington, N.Y.