# Solve Equation for Remaining field

**Kris**Hey guys, I made my first form/calculator and I am having issues with a couple things. How can I make it so that if a value isn't entered into a field, the calculator will still solve the problem by skipping the blank fields? In example, my form below is a nice handy calculator but there is not always a sprocket reduction in all configurations. If blank, the equation should still solve and just leave it out but instead it never solves.... Or have the option to check a N/A box to leave that entry out.

http://form.jotform.us/form/50120164021130

My other question is, how do you make it so that the equation will solve for the missing value. Kind of how a lot of triangle calculators work. You only need to know any 3 values of a triangle to find the other 3 values. That way I could enter in desired Feet per minute, Motor RPM, Motor Gear Ratio, Pulley sizes, and solve for possible sprocket combinations, or otherwise solve for Pulley Sizes, gear reduction, or FPM.

Thank you for any help.

Kris

- JotForm Support
**TitusN**Hello Kris,

Javascript (which is used to read/calculate values on your form )reads empty fields as null when there is no value - so a value needs to be defined - either a "1" or "0" so that the value gets passed to the calculation fields.

But we have to begin from the start.

Kindly share your basic equation as to how your form should work - it will help us understand your requirements and address your questions on how to configure the form to give accurate answers.

I hope the equation is linear :-) But share if anyway even if its not.

I'm thinking its possible to make your form such that it would work in the following way:

1. Read unentered values and still pass a result

2. Solve and update missing values regardless of which has not been filled out.

Looking forward to your response.

**Kris**the equation I used to solve for final feet per minute:

(Motor RPM/Gear Ratio*(Motor Sprocket/Shaft Sprocket))*(Drive Roll/Driven Roll)*(Driven Roll/3.82)=SFPM

**Charlie**Hi,

I cloned your form and edited it. Here's the edited one in my end: http://form.jotform.us/form/50120164021130. When one of the field is not greater than 0, then the end result in SFPM would always be "0". Let's say Motor RPM is left out, the default value will be "0", and 0 / Gear Ration is equal to "0" then multiply to a couple of fields will also end up to "0".

I presume that what you would like is that when a field has a missing value, it will then act as the "result" field. Example: If Motor RPM is left out but others are not (including SFPM), using the formula as a basis, the form will calculate the Motor RPM as the result output. Is that correct? If that is the case, we can use

**"Conditions"**to setup a logical form together with the use of Form Calculation widgets and other functions, but the formula for all of the fields that would will use a triangulation calculator or formula will of course be coming from you, I'm not that familiar with Feet Per Minute or something related to it.You could, however, enlighten us and give us sample calculation so that we can help you better on building this form, this seems to be a challenging one though.

We'll wait for your response.

**Kris**Well really, since I am looking to solve for the missing value; I would need to have an option to "disable" a section of the formula. For instance, not all configurations have a motor sprocket or shaft sprocket. Therefor the formula should read: (Motor RPM/Gear Ratio)*(Drive Roll/Driven Roll)*(Driven Roll/3.82)=SFPM with (motor Sprocket/shaft sprocket) left out. Is there a possibility to have a check box to disable a "component"?

I can easily come up with the formulas to solve for each missing value, would just need to know how to incorporate that into the form.

**raul**You can also use conditional logic to accomplish this.

Please take a look at this demo form: http://form.jotformpro.com/form/50126338148957I've added a radio button (so only one field can be disabled, but you can use checkboxes in case you want to allow more than one field to be selected).

Please let us know if this what you mean when you say you want to "disable" a section of the formula or if you're referring to something else.

Thank you.

**Kris**So. Motor RPM, Gear Ratio, and Driven Roll will always be used. I would like an option to select which components are or are not in use thus modifying the formula.

So if Motor RPM, Gear Ratio, Motor Sprocket, Shaft Sprocket, Drive Roll, and Driven Roll are all in use the formula would be

(Motor RPM/Gear Ratio*(Motor Sprocket/Shaft Sprocket))*(Drive Roll/Driven Roll)*(Driven Roll/3.82)=SFPM

if Motor RPM, Gear Ratio, Drive Roll, and Driven Roll are in use (motor sprocket and Shaft Sprocket disabled) the formula would be

(Motor RPM/Gear Ratio)*(Drive Roll/Driven Roll)*(Driven Roll/3.82)=SFPM

if Motor RPM, Gear Ratio, motor sprocket, Shaft Sprocket, and driven roll are in use (drive roll disabled) the formula would be

(Motor RPM/Gear Ratio*(Motor Sprocket/Shaft Sprocket))*(Driven Roll/3.82)=SFPM

Those are the only 3 combinations usually used.

I would still like to know how I can set it up so I could enter Motor RPM, Gear Ratio, Motor Sprocket, Shaft Sprocket, Drive Roll, and Driven Roll and then leave SFPM blank and the form will solve for SFPM

Or enter Motor RPM, Gear Ratio, Motor Sprocket, Drive Roll, Driven Roll, and SFPM and then leave Shaft Sprocket blank and the form will then solve for Shaft sprocket.

Make sense?

- JotForm Support
**Mike**It is possible to use different formulas with 'Update a form field value' conditions on form. Please take a look at the following animation to get the idea:

So you can try to add three conditions with different formulas to see if it works in your case.

If you need any further assistance on this, please let us know. Thank you.