I made an assumption you are using at least SQL Server 2000.

DECLARE @Temperature TABLE (CalendarDate datetime, Temperature decimal(10,2),UOM char(1))

INSERT INTO @Temperature

SELECT GETDATE(), 55, 'F'

UNION ALL

SELECT GETDATE(), 15, 'C'

UNION ALL

SELECT GETDATE() + 1, 58, 'F'

UNION ALL

SELECT GETDATE() + 2, 60, 'F'

UNION ALL

SELECT GETDATE() + 3, 14, 'C'

SELECT

CalendarDate,

MAX(CAST(CASE WHEN UOM = 'F'

THEN Temperature

WHEN UOM = 'C' THEN (Temperature * 1.8000) + 32.00

END AS DECIMAL(10,2))) AS Fahrenheit

FROM

@Temperature

GROUP BY

CalendarDate

SELECT

CalendarDate,

CAST(CASE WHEN UOM = 'F'

THEN Temperature

WHEN UOM = 'C' THEN (Temperature * 1.8000) + 32.00

END AS DECIMAL(10,2)) AS Fahrenheit

FROM

@Temperature

-- I think this will give you what you are looking for:

SELECT

t.CalendarDate,

CAST(CASE WHEN t.UOM = 'F'

THEN t.Temperature

WHEN t.UOM = 'C' THEN (t.Temperature * 1.8000) + 32.00

END AS DECIMAL(10,2)) AS Fahrenheit

FROM

@Temperature t

inner join (select t1.CalendarDate, max(t1.UOM) UOM from @Temperature t1 group by t1.CalendarDate)dt

on (t.CalendarDate = dt.CalendarDate and t.UOM = dt.UOM)

ORDER BY

t.CalendarDate;