# About multiplication depth

**URL:** <https://openfhe.discourse.group/t/about-multiplication-depth/1198>\
**Category:** FHE Questions\
**Created:** [April 16, 2024, 8:21am UTC](https://openfhe.discourse.group/t/about-multiplication-depth/1198 "2024-04-16T08:21:58Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![kenan](https://avatars.discourse-cdn.com/v4/letter/k/e495f1/32.png) [@kenan](https://openfhe.discourse.group/u/kenan)\
**Post date:** [April 16, 2024, 8:21am UTC](https://openfhe.discourse.group/t/about-multiplication-depth/1198/1 "2024-04-16T08:21:58Z")

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I would like to ask the following questions  
Can ciphertexts with different multiplication depths be compared, or is it necessary to have a uniform depth.  
How to reduce to a unified custom ciphertext multiplication depth？

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<div class="post-metadata">

**Author:** ![andreea.alexandru](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/andreea.alexandru/32/378_2.png) [@andreea.alexandru](https://openfhe.discourse.group/u/andreea.alexandru)\
**Post date:** [April 16, 2024, 4:29pm UTC](https://openfhe.discourse.group/t/about-multiplication-depth/1198/2 "2024-04-16T16:29:13Z")

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All operations between ciphertexts should happen on the same number of limbs and the same depth/scaling factor, because both ciphertexts should have the same modulus.  
The AUTO modes take care of this implicitly. For FIXEDMANUAL, you need to call ModReduceInPlace.

For instance,  
c = cc-\>EvalMult(c, c);  
cc-\>ModReduceInPlace(c);

FIXEDMANUAL should be used by advanced users, since the user is responsible for tracking the number of limbs and scaling factor of the ciphertexts.