Text Field To Number Issue

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We have a reporting requirement that is giving me trouble.  We have a custom test field that is populated with a duration in either whole numbers or decimal.  For example, values could be 1, 2.5 or .5 etc but will not have more than one decimal place so I converted it to a number and used the functions in this post https://cx.rightnow.com/app/answers/detail/a_id/5570. 

This function to_number(incidents.c$custom_field) + to_number(substr(incidents.c$custom_field, instr(incidents.c$custom_field, '.') + 1))/100 results in the actual number being changed as seen in Duration1 column of attachment.