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Consider part of the web page below:

enter image description here

Currently Users can add new rows and and enter values, which are either various numbers that are considered as English Units upon entry. i.e. feet, inches, and so on.

Features:

I am working towards adding UI elements that will drive this system behavior:

  • Ability to switch the mode of entry from English to SI system, and back

I am thinking of adding a "toggle button" that says "Switch to SI" (when current entry mode is English), or "Switch to English" (when current mode is SI). Doing so will also recompute all existing fields from one system to another as to reflect the current chosen state. And by the toggle button say "Currently working in SI/English Units"

This seems to me as a workable option, but I wondered if it can be made better or simpler. I am a bit concerned about recomputing all the fields upon toggle as that can be a source of rounding errors after a while, but that can be offloaded to the technical implementation instead of UI and not considered here. I am also concerned that users may be getting confused at times, since they are looking at a wall of numbers, and they'd have to look at the "current state" wording somewhere else to remind themselves which "state" they are in.

How do I design an effective UI that lets the user feel they have the "I want to be able to switch the unit system when entering / editing data".

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Regarding the rounding error, if you store in the unit they entered initially (or as a single type of unit), and then convert on display, you should only get a small rounding error but it shouldn't be compounded.

Regarding the switch, I think the answer depends on why people would be switching back and forth between units. Wouldn't they typically just use one unit? In any case, I don't think you'd need a toggle switch but instead a dropdown:

Dropdown

You could instead use tabs above the field set ("English" and "SI")

  • we deal with international clients, and their spec comes in one system or another .... our staff has to convert SI to English whenever they get SI units – Dennis Jul 28 '14 at 21:11
  • can you give me more info on why you've chosen to use a dropdown, opposed to any other possible way of selecting a unit system of measurements? i.e. I can think of a radio button choice as well. – Dennis Nov 6 '14 at 17:44
  • Radiobuttons take up a lot of space and except for standard forms are almost never the right choice. Dropdowns hide all of the choices except the one you have selected (or the default). That both makes it clear what state you have selected while also making the tool feel less complicated. – Paul Nov 7 '14 at 18:06

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