Lineman's Reference - XFMR LAB
by Digital Apprentice LLC
- Education
- Paid
- Small & simple · 80
- Rating
- 4.7
- 395 ratings
- Top 77%among 226 Education apps
- Last update
- Sep 1, 2026
- Version 2.0.6
- Size
- 68 MB
- Category
- Education
- Tracked since
- Oct 10, 2026
Estimated revenue
A model estimate with a likely range, not a reported figure.
No estimate. Apps outside the grossing charts, and some countries, have no reliable rank-to-revenue curve, so we show nothing rather than a guess.
How this estimate is made
Rank: we take the app's best Top Grossing rank on the latest chart day. Category ranks are converted into an equivalent overall rank, because a #10 in Finance earns far less than a #10 overall.
Curve: that equivalent rank is read off a rank-to-revenue curve anchored on public company revenue and market-data reports for the US iPhone App Store.
Country: the curve is scaled per country (Japan is roughly a third of the US, Türkiye under 1%). Where we have no scale, such as China, there is no estimate.
Range: the likely range widens with country, category and chart depth. It is a plausible span, not a statistical confidence interval.
Not included: ads, payments outside the App Store, and any difference between gross sales and what the developer keeps. Low confidence means indirect data; medium means several independent sources agree.
Full methodScreenshots
As shown on the App Store listing.
About this app
Text from the App Store listing.
Learn it. Wire it. Energize it. Check your work.
Built by a working journeyman lineman for linemen and their apprentices. The XFMR Lab simulates distribution transformer banks driven by your own wiring — the metering, fusing, and faulting all behave the way you'd expect in the field.
NEW IN 2.0 — BUILT-IN TRANSFORMER TRAINING (Replacing XFMR INFO)
Six guided lessons take you from "what's a transformer?" to wiring a 3-pot bank:
- Start Here — What is a Transformer?
- Dual H Bushings — The Two Wirings & the Nameplate
- The Tap Changer — One Pot, Multiple System Voltages
- Three-Phase — The Three Phases and How They're Related
- Bank Identification — Delta or Wye, Open or Closed
- Your First Bank: Delta-Wye Closed (120/208)
- More lessons on the way!
Work the lessons in order, or jump straight to the labs.
ALSO NEW IN 2.0
- The Sandbox (Beta) — wire anything from scratch in a COMPLETELY-customizable lab, with live, vector-based voltage and fault logic baked in.
- Death Traps — scenario-based transformer traps linemen run into — and how to navigate them safely.
- A brand-new look across every lab — new graphics, sharper, faster, & easier to read in the field.
- Voltmeter you can now drag with two fingers; readings update as the leads move.
- Parallel the secondary coils by hand in wye secondary labs
- Stats that track lab completions, quiz scoring and for-fun stuff like the number of fuses you've blown.
- User Customizations - the user can now alter the spec of their labs; from grounding to parallel coil cutover-direction, requiring the 4th cutout, tap changer implementation and more.
- 2.0 is FREE for everyone who already owns XFMR Lab — thank you for years of feedback and encouragement.
WHAT YOU GET
Single Phase — Single Bushing · Dual Bushing
Three Phase (closed) — Delta-Delta · Delta-Wye · Wye-Delta · Wye-Wye
Three Phase (open) — Open Delta-Delta · Open Wye-Delta
Misc — Paralleling · 4th Cutout · Death Traps (6 Scenarios)
Advanced — Straight 480 · 240/480 · 277/480 · Corner-Grounded 240/480 · Wye-Wye 5-Wire (120/240 + 120/208) - all now able to be wired up Wye AND Delta on the topside
The Sandbox (Beta)
EVERY FUTURE UPDATE IS FREE - THE APP IS A ONE-TIME PURCHASE. I'm always working on new updates.
TOOLS & REFERENCE
- Volt, ohm and rotation meters with real behavior
- Nameplate, secondary coil and tap changer animations
- Reference diagrams for every standard bank
Learning Mode walks apprentices through every wrong-connection check. Journeymen and experienced users can keep this turned off if they'd like.
QUIZZES
- Classic Quiz — Select each lab you want in your quiz - with graded scoring across each lab.
- Advanced Quiz — You're provided with the job-site info and need to pick the right nameplate and coil setup, then wire it.
- Bank ID - A beginner's quiz tied into the new XFMR Training lesson plan. The user is provided with different primary and secondary wirings and must correctly identify them.
Used by 30,000+ linemen since 2021.
Questions? Suggestions? Reach me at [email protected]
What’s new
Release notes for the latest version, as written by the developer.
Various bug fixes and feature polishing.
Rank history
Daily position in the US charts. #1 is at the top.
- Best rank
- #8
- Current rank
- #14
- Days charting
- 7 of 7
On the charts today
Small & simple score
How realistic it is for a small team to build something like this.
80/100
Small & simple
- Developer size70% · 25
Developer: 2 apps on the charts
- Audience size100% · 20
Ratings: 395
- App size60% · 10
Size: 68 MB
- Price model100% · 15
Price model: paid
- Demand proof70% · 30
Best rank #8, 4 countries
An indicator, not a fact. We can't see team size. Calculated Oct 25, 2026 · method i2
How the score worksGap check · UK
Is this US chart app missing in UK?
Median rank and days in the top are part of Pro.See Pro
Store check Oct 22, 2026
This is a candidate, not a verdict. Charts show at most 100 apps, so not charting does not mean no demand. Check the UK store before you decide.
See all gapsVersion history
- 2.0.6LatestReleased Sep 1, 2026