[Milsurplus] BC-221Tempature compensating Capacitors question

[John Hutchins]

Group -

If I were to replace the 6pF temperature compensating capacitor on the 
1000KHz crystal reference Oscillator with what would I replace it dear 
Lizor, with what?
The Crystal Reference Oscillator starts high 1220KHz. As the unit warms 
up after 2 hours the Crystal Oscillator comes down to 1000KHz +20 -0 Hz

What does N mean? Negative Capacitance? N30 means -30%
What does NPO mean, stable at any temperature?
Thanks
Hutch

TEMPERATURE COMPENSATING
NPO
N30
N60
N80
N150
N160
N220
N470
N750
N4700

I found these specifications:
NPO Specifications:
• Temperature coefficient: ±30 ppm
• Temperature range: -55°C to +85°C

SL Specifications:
• Temperature coefficient: -700 + 350 ppm
• Temperature range: -55°C to +85°C

Y5P Specifications:
• Temperature Range: -30°C to +85°C
• Dissipation Factor: 2.5%
• Standard Tolerance: ±10%

Z5U / Z5V Specifications:
• Temperature Range: +10°C +85°C
• Dissipation Factor: 5%
• Standard Tolerance: ±20% or +80%-20%