Recommendation letters when changing between two unrelated fields I was a humanities major in undergrad and am now applying for a master's in engineering. The program I'm considering is a three-year MS that explicitly targets students without engineering backgrounds. To apply, all they require is proficiency in first-semester calculus. Besides a stats elective and AP credits, I didn't take formal math courses in college, but since graduating, I've self-studied the calculus sequence and differential equations, and I am currently working on linear algebra.

My concern is with getting letters of recommendation that will be relevant to the admissions committee. I have one recommender, my undergraduate thesis advisor, who can attest to my research skills and time management. For the second letter, I think it would be ideal to have someone who can speak to my math ability, as I can imagine that admissions will regard my self-study with skepticism. However, I've been out of college for a year and a half and now work overseas, so seeking a reference from someone in my university's math department is impractical.

Do you have any ideas for how someone in my situation could get a letter of reference from someone who can directly address my potential as an engineer?

Failing that, or perhaps in addition, can you suggest any concrete ways I can demonstrate my math ability to the admissions committee?

I've taken a look at these two questions:


Who to ask for letters of recommendation when changing fields after PhD?
When changing fields from undergrad to PhD, which department should recommendation letters come from?


I believe my question is distinct since I am looking to make a much more drastic switch between fields, and my competitors are also people who are changing fields.

Both my undergraduate institution and the graduate program in question are in the US.
If someone in your undergrad math department has actually evaluated your work, then the year and a half is not an obstacle for a recommendation. Best if they know you as more than a body who occupied a seat, of course. 

But in general, if no one has seen your work, nor had a chance to evaluate it, then they can't really attest to it, ethically or practically. 

Since your situation is described as a bit unique, let me suggest, at least, a unique solution. You could ask a mathematics professor, either at your original institution or elsewhere, to evaluate your skills. There are at least two ways that could be accomplished. They could just give you a final exam from some recent course and decide whether you have the skills. But a fifteen minute or so oral exam should be enough to get an idea. They could then, simply certify about what they did and how you did. It wouldn't be a real letter of recommendation, perhaps, but might fulfill your needs. 

An alternative is just to suggest to an admissions committee that you would be willing to take such an exam if there is any doubt about your qualifications. That alone might be enough. 

Thirdly, nothing at all might be needed. The program seems pretty flexible. Perhaps flexible enough to accommodate your self study as valid.