CastorPrep

The AI tutor

Castor — a tutor that's already worked the problem

Grounded in verified worked solutions and the NCEES Reference Handbook — not in whatever the internet thinks.

How it works

Grounded, start to finish.

Stage 1

An authored problem

Every problem in the bank is original and written to the exam's own blueprint — the same areas, the same depth of calculation, the same Handbook dependence you'll face on exam day.

Stage 2

A verified worked solution

Before a problem goes live, it carries a full worked solution: the governing relation, each intermediate value, the Handbook section every number comes from, and why each wrong option is wrong.

Stage 3

Castor answers from that solution

When you ask Castor anything, it teaches from that verified work — purpose-built on frontier AI, scoped to the problem in front of you, citing the Handbook sections you'd flip to at the testing center.

What it does

Three jobs, done properly.

Explains your miss

“You picked B — here's the step where B diverges.” Castor names the specific error that produces each wrong option, because the authored solution records it.

Cites the Handbook

Every reference points at the section you'd flip to on exam day — so each problem doubles as a rep at finding the value under closed-book CBT conditions.

Talks you through when stuck

Before you answer, Castor works in coach mode: it probes your setup, checks intermediate steps, and hands out graduated hints — one nudge at a time — while the final call stays yours.

Castor— AI tutor

Coach mode, before answering — a psychrometric sketch: match four processes to their arrows.

Where do I even start with this one?
You have four common air-conditioning processes. For each one, ask yourself: what happens to dry-bulb temperature, and what happens to the humidity ratio (W)? Those two things alone will tell you the direction of the arrow. Pick one process — say, sensible heating. What would you expect to happen to db and W when you add heat without adding or removing moisture?
Evaporative cooling, I think? It drops the dry-bulb and the moisture stays put.
Not quite. Evaporative cooling does drop the dry-bulb — that part's right. But what about the moisture? When you evaporate water into the air, does W stay the same, or does it rise?
Ah — the water going in has to raise W. Look, can you just give me the four matches so I can check my work?
I'll walk through it with you after you submit, no problem. But right now, let's finish nailing down evaporative cooling first — you're almost there. So evaporative cooling raises W and lowers db. Now look at the four arrows: which direction on a psychrometric chart means db falls while W rises?

A real coach-mode exchange with Castor, on a live problem from the bank. The final call stays yours.

What it won't do

Castor won't do your thinking for you. Before you answer, it coaches — it won't hand you the letter. It's scoped to the problem in front of you and your own work, because a tutor that answers everything is just a chatbot, and chatbots don't get you licensed.

Use it freely

On every problem, in every plan.

Castor is included in every plan — no meters, no per-question credits. Ask as much as your studying needs, on every problem in the bank.

Start your free trial

7 days, no credit card.