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Supplementory Income Statement (Tables)
12 Months Ended
Dec. 31, 2019
Notes to Financial Statements  
Supplementary Income statement
   Year Ended December 31,
   2019  2018  2017
Maintenance and repairs  $29,000   $47,000   $38,000 
Production taxes   203,000    242,000    154,000 
Taxes, other than payroll and income taxes   18,000    14,000    11,000