I need an app developer for android

General information for the business: Native Android app in java.
Kind of development: New program from scratch
Description of requirements/functionality: I wish to have a very simple app made for android and iPhone. It will be a type of calculator. It is to calculate weights of diamonds. The weight is measured in carat (ct). So when I type in the millimetre diameter eg 1.3 if I have 30 diamonds 1.3mm in size I will do 1.3 DIA x 30 =RESULT.
When I type 1.3 as the diameter the default number is the weight of the 1.3 diameter diamond. So
Type 1.3 (actual equitable number 0.95) press DIA then x 30 (amount of diamonds) = 28.5ct

The image shows the calculation and how it is to be displayed. The keypad configuration can differ.
I wish the display to show 1.3 in blue (all diamond sizes to be in blue) ie I type 1.3 then press DIA and the 1.3 then it turns blue to denote it is the diamond measurement next to it is displayed the actual individual weight 0.95ct
All weights will be given and will be for gemstones 0.6mm to 4.0mm in 0.1mm increments.

All other functions displayed are to be active and work as intended as with normal calculator.
Extra notes: