# Circle Diagram — Circle Diagram for VT

> Circle Diagram for VT (iPhone/iPad app by Keiichiro Nakagawara.)

- Source: https://appshunter.io/ios/app/circle-diagram/id6462698792 (this page in markdown: same URL + `.md`)
- Developer: [Keiichiro Nakagawara](https://appshunter.io/developer/1577061939)
- Category: Education
- Price: $0.99
- Age rating: 4+
- Requires: iOS 15.0 · 3 MB
- Languages: English, Japanese
- Released: 2023-08-21
- Data updated: 2026-07-22
- User reviews in markdown: https://appshunter.io/ios/app/circle-diagram/id6462698792/reviews.md

## What is Circle Diagram?

Circle Diagram is an easy-to-use app that can show the circle diagram of instrument voltage transformers given their zero burden error and rated burden error. And it enables you to get their error with an arbitrary burden you would connect to their secondary terminals. Error means ratio error and phase angle error of instrument voltage transformers. The zero burden error is one of their errors with the secondary terminals open. The rated burden error is one of their errors with the secondary terminals connecting to the rated burden.  You can move a pointer within the error circle on the diagram and get the burden and the power factor with the arbitrary burden error. The main screen is shown in the figure 1. It has a circle diagram with ratio error on the x-axis and phase angle error on the y-axis. And it has the zero burden and its error TextFields, the rated burden and its error TextFields on the bottom and the arbitrary burden TextFields and its errors on the top. The zero burden and the rated burden and their errors is used to calculate the circle. You can get the error with the arbitrary burden and the location of the pointer which means the ratio error and the phase angle error on the diagram. The line, pointer and letter color on the diagram could be changed into the color you would like in the settings Action Sheet which could be shown by tapping the Settings Icon. The line width on the diagram could be changed also in the sheet. 

Features:

X-Axis Range:  ±0.2, ±0.4, ±1.0, ±2.0%
Y-Axis Range:  ±6.9, ±13.8, ±34.4, ±68.8 minutes 
Least Significant Digit:  0.01, 0.001


## Version history (last 3 releases)

### 1.2.0 — 2024-03-25

The bug that the alert always appears when you input any data in the arbitrary burden textfield. The Least Significant Digit can be selected from 0.01 and 0.001. The x-axis range of the diagram can be selected from one of the following: ±0.2, ±0.4, ±1.0, and ±2.0%  which are approximately equal to ±6.9, ±13.8, ±34.4 and ±68.8 minutes on the y-axis.

### 1.1 — 2023-08-21

The arbitrary burden and its error can be saved. When the app is started, the arbitrary burden and its error at the time the app was terminated is displayed.

### 1.0 — 2023-08-21

No release notes.

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## More apps by Keiichiro Nakagawara

- [W Generator](https://appshunter.io/ios/app/w-generator/id1577061937)

All apps by Keiichiro Nakagawara: https://appshunter.io/developer/1577061939

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-07-22.*